Updates theme names to be compatible with Godot 3.5 (no spaces),
consistent with other Godot theme item names (snake_case), and
match the color names listed on the
[ANSI escape code wikipedia page](https://en.wikipedia.org/wiki/ANSI_escape_code#3-bit_and_4-bit).
Deprecates the old names and warns users to change them.
Keeps the archive small and licensing simpler.
Keep around the fancy fonts such as Noto Color Emoji and Unifont as they
are useful for testing.
With the xrdb import plugin making it easy to import themes, there is
little point in keeping other pre-defined themes around, so remove
these.
Replaces default.tres, default_dark.tres, and default_light.tres, with
default.tres and default_light.tres based on Godot's default dark and
light editor themes respectively.
Closes#44
