Add custom theming support

[vl-ms]

I LOVE this keyboard! It is one of those productivity boosters that I NEED on my phone. There is only one problem: it's styles don't fit with Solarized Termux, so I had to change the default theme to a pure black theme, which is not as easy on the eyes as Solarized is for me. As other people love other colorschemes, I think it is extremely important to add at least basic support for this feature, like a specific setting where you can define your own theme, and export it.

[OmlineEditor]

I think you need to allow the user to make their own theme and choose the keyboard color on their own. we need a full customization of the appearance by the user himself

[vl-ms]

it would also be nice to be able to move some keys around. E.g. I use vi* a lot, and I am right-handed, so if shift could be moved to the right my fingers wouldn't need to stretch nearly as much as they need to right now. Also, custom keys with commands akin to https://github.com/adgad/kboard might be useful for repetitive actions. but that might be much harder to implement right.

[OmlineEditor]

it would also be nice to be able to move some keys around.

I offered to do it in this ticket https://github.com/Julow/Unexpected-Keyboard/issues/231 , there is a link to a program that allows you to do it, but I would like to implement it in this program. complete freedom of action is what you need for a good keyboard

[Julow]

Custom themes are high on my TODO list (also more and better pre-defined themes). If someone consider doing this, there's some inspiration to take from https://github.com/Julow/Unexpected-Keyboard/pull/102 (it defines many of the colors/sizes options as well as drawing borders around keys and other things unrelated to theming).

[eeriemyxi]

As a temporary workaround, key and background opacities can be utilised to get a matching background.

One can use Lucky Patcher's "Clone application" feature to install the same keyboard twice and use one with the workarounds just for Termux in case they find the opacity hard to use in other apps. This is untested, so might not work though.

[Secret-chest]

I really need this as well.

[Spike-from-NH]

@vl-ms, moving keys around, including turning swipes into standalone keys, can be done with custom layout XML, which Julow taught me how to use in #354, or the web tool that @OmlineEditor mentions above.