add input:kb_file option to use a .xkb file.

[FlafyDev]

Describe your PR, what does it fix/add?

The PR adds an option to add a .xkb file as your layout instead of using the existing 5 xkb options.

When the option is set to a valid file, it doesn't use the other xkb options.
When the option is set to null or fails, it uses the other xkb options.

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

• I created a function called absolutePath in order to reduce duplicated code but wasn't sure where to put it so I kept it in ConfigManager. This is probably not smart to do, but because I'm not familiar with c++, I wasn't sure where to put it.

Is it ready for merging, or does it need work?

From what I tested it works.
Tested:

• When the option is set to null
• When the option is set to a full path
• When the option starts with ~
• When the option points to a non existing file (silently fails)

[vaxerski]

pretty nice cutie, just one thing: move the absolutePath func to miscfunctions.cpp, and add another param for the cwd instead of configCurrentPath

[FlafyDev]

Done. I had to make configCurrentPath public, though.

[vaxerski]

lgtm. Thanks!