Terminal: Fix translation of "Colors" window title

Change-Id: I9a9f166dbdb4a2e008eabab53c9ab70f3439aa59
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6899
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

Terminal: Menu "Theme settings..." -> "Colors..."

"Colors" is simpler, better translatable and currently more
correct. A "theme" is broader, including backgrounds, fonts,
mouse cursor, sounds etc.
For a Terminal it's mostly colours. Fonts are being handled in
the "Settings" panel.

Change-Id: Icf043fffbc64d976db7a71c28c41aeea0cdf44e6
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5999
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

Terminal: graphical settings for configuring themes.

Implements #16835: Make colour schemes modular.
Implements #15936: Terminal settings should allow to drop a colour.

Change-Id: I1071c9285ba887e734af47b724f9de7f6c660581
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5950
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>