Add basic .xrdb/.Xresources import plugin

Adds basic support for importing .Xresources and .xrdb files as Theme
resources.

Examples of terminal color schemes in .xrdb format can be found here:
https://github.com/mbadolato/iTerm2-Color-Schemes/tree/master/xrdb

Examples of terminal themes in .Xresources format can be found here:
https://github.com/mbadolato/iTerm2-Color-Schemes/tree/master/Xresources

https://terminal.sexy also supports exporting themes is Xresources
format.

addons/godot_xterm/import_plugins/xrdb_import_plugin.gd

@@ -0,0 +1,122 @@
+tool
+extends EditorImportPlugin
+
+const XrdbTheme := preload("../resources/xrdb_theme.gd")
+
+
+func get_importer_name():
+	return "godot_xterm_xrdb_importer"
+
+
+func get_visible_name():
+	return "xrdb_theme"
+
+
+func get_recognized_extensions():
+	return ["xrdb", "Xresources", "xresources"]
+
+
+func get_save_extension():
+	return "res"
+
+
+func get_resource_type():
+	return "Theme"
+
+
+func get_import_options(preset):
+	return []
+
+
+func get_preset_count():
+	return 0
+
+
+func import(source_file, save_path, options, r_platform_variant, r_gen_files):
+	var file = File.new()
+	var err = file.open(source_file, File.READ)
+	if err != OK:
+		return err
+
+	var theme: Theme = XrdbTheme.new()
+	theme.default_font = preload("../themes/fonts/regular.tres")
+
+	var word_regex = RegEx.new()
+	word_regex.compile("\\S+")
+
+	var color_regex = RegEx.new()
+	color_regex.compile(".*(?<name>cursor|foreground|background|color\\d+):")
+
+	while not file.eof_reached():
+		var line = file.get_line().strip_edges()
+		var words = word_regex.search_all(line)
+		if words.size() < 2:
+			continue
+
+		var name: String
+		var color: Color
+
+		if words.size() == 2:
+			if "cursorColor" in words[0].get_string():
+				name = "cursorcolor"
+				color = Color(words[1].get_string())
+			else:
+				var c = color_regex.search_all(words[0].get_string().to_lower())
+				if c.size() > 0:
+					name = c[0].get_string("name").to_lower()
+					color = Color(words[1].get_string())
+
+		if words.size() == 3 and words[0].get_string() == "#define":
+			name = words[1].get_string().to_lower()
+			color = Color(words[2].get_string())
+
+		if not name or not color:
+			continue
+
+		match name:
+			"color0", "ansi_0_color":
+				theme.set_color("Black", "Terminal", color)
+			"color1", "ansi_1_color":
+				theme.set_color("Red", "Terminal", color)
+			"color2", "ansi_2_color":
+				theme.set_color("Green", "Terminal", color)
+			"color3", "ansi_3_color":
+				theme.set_color("Yellow", "Terminal", color)
+			"color4", "ansi_4_color":
+				theme.set_color("Blue", "Terminal", color)
+			"color5", "ansi_5_color":
+				theme.set_color("Magenta", "Terminal", color)
+			"color6", "ansi_6_color":
+				theme.set_color("Cyan", "Terminal", color)
+			"color7", "ansi_7_color":
+				theme.set_color("Light Grey", "Terminal", color)
+			"color8", "ansi_8_color":
+				theme.set_color("Dark Grey", "Terminal", color)
+			"color9", "ansi_9_color":
+				theme.set_color("Light Red", "Terminal", color)
+			"color10", "ansi_10_color":
+				theme.set_color("Light Green", "Terminal", color)
+			"color11", "ansi_11_color":
+				theme.set_color("Light Yellow", "Terminal", color)
+			"color12", "ansi_12_color":
+				theme.set_color("Light Blue", "Terminal", color)
+			"color13", "ansi_13_color":
+				theme.set_color("Light Magenta", "Terminal", color)
+			"color14", "ansi_14_color":
+				theme.set_color("Light Cyan", "Terminal", color)
+			"color15", "ansi_15_color":
+				theme.set_color("White", "Terminal", color)
+			"foreground", "foreground_color":
+				theme.set_color("Foreground", "Terminal", color)
+			"background", "background_color":
+				theme.set_color("Background", "Terminal", color)
+			"selection_color":
+				theme.set_color("Selection", "Terminal", color)
+			"selected_text_color":
+				theme.set_color("Selected Text", "Terminal", color)
+			"cursorcolor", "cursor_color":
+				theme.set_color("Cursor", "Terminal", color)
+			"cursor_text_color":
+				theme.set_color("Cursor Text", "Terminal", color)
+
+	return ResourceSaver.save("%s.%s" % [save_path, get_save_extension()], theme)