Req: icon for button: allow to pick more TC4A icons

[DrShark]

TC already allows to select some internal icons for button in "Internal command" icons cartegory.

I suggest to add another category where user will be able to select other icons that included in TC4A package.
For example, this way user could directly pick "command line" icon used for "Send shell command" type of a button, or to pick icons from different TC themes for different types of memory (internal and memory card(s), and same-named folders there, like Photos.)

Yes, it's already possible to use all icons from TC package by unpacking TC's APK file, but this way is not so convenient and requires additional storage space.