add indentation options to kate

[Asqiir]

This is the first contribution to #87 .
It allows users to configure the way kate handles indentation.

Reasoning about decisions:

I decided to put all options into config.programs.kate.editor. The editor option should contain all options that act on configuration into the rectangle where users type text in (as opposed to: the console, the project tab, the menus and sidebards).

Known limitations:

• kate needs to be restart after switching the configuration. I could not figure out how to make kate do a hot reload on the changed katerc.
• I would like to have the message in the assertion reference the variables in question not hard-coded by their name. I would prefer if the compilation fails if someone was to change the names of the variable but forgot to update the message.

Do you want me to put all changes into a single MR (leaving this one open), or do you prefer each change to be its own PR?

[magnouvean]

See my two small comments. Looks good to me otherwise assuming you have tested that the module works (I don't really use kate so I can't really test)

[Asqiir]

found bugs :(
(do not merge yet, I hope to fix it today)

fixed

[magnouvean]

I added an enable option (which is in general good practice) and assigned config.programs.kate to a variable cfg (which we do throughout the project to shorten things up a bit). See my two earlier commits. Are you happy enough with this so that we can merge this now @Asqiir?

[Asqiir]

@magnouvean we can merge this imo