Adds an option to the script editor context menu that lets you open
a ColorPicker in order to easily edit `Color()` constructors.
To do this, right click on the word `Color` and select `Pick Color`.
A side effect of this change is that the script editor now has its own
context menu instead of re-using the one from TextEdit.
It's now possible to indent left/right and to toggle comments via this menu.
I also felt free to make it more context-sensitive than before:
Now "Cut" and "Copy" will only be shown if text has actually been selected.
I also added default shortcuts for indent left/right. (alt + left/right)
Closes#6232
