[Feature] Add English GB language support

[chip33]

Here is an English GB language resource file for adding to STM.

Only "Customize" and several uses of "Color" needed changing for en-GB.

lang.en-GB.resx.txt

It was previously discussed here where some possible modifications to the English language strings in STM are also discussed.

[Hofknecht]

@chip33 Thank you for the feedback! Now en-GB available and also your suggestions from #402 included

[chip33]

Thank you, works very well. :)