Sorting themes and some design changes

[txtyash]

I like your script and what's really cool about it is that it works on most terminals regardless.
I'm not trying to be rude, these are just some suggestions.

I'm proposing 2 changes:

1. Keeping themes separate from the source file
2. Copying design changes from gelacritty
   • replacing cmd line options with ones similar to gelacritty's(Can be seen by running gela h)
   • an interactive menu similar to gelacritty's when it is run with just gela

I'm sorry if the issue sounds irrelevant. Feel free to close. But, in case you liked my suggestions I will also be freed from having to maintain my script and use theme.sh everywhere.