Start using IDEA

This currently only includes gitignores and a startup script, not my
IDEA config, because that's far from finished.
Tidy x-peripherals.sh a bit

Because there's a keyboard setup update incoming… :D
Make have_xinput a function
Advanced keyboard config including Apple keyboard

This uses Caps Lock as Compose key and changes the modifier keys right
to the space bar on my Apple keyboard. Additionally, F13 is Print and
F15 is Insert.

Furthermore, the "zap server" option moved out of .xinitrc and into
x-peripherals.sh, which will be called from there anyway. This is
because setxkbmap resets xmodmap and I want to keep confusion and
breakages because of run order problems to a minimum. ;)

Now the next thing I want is to have Apple's special keys on Alt Gr or
something like that…