Made all header files to have LABWC_ prefix in include guard identifers.
Converted from __LABWC_ in 35 include/ files.
Converted from __LAB_ in 5 include/ files.
Added LABWC prefix to 3 include/ files.
Added include guards to 3 include/ files.
The double underscores were removed since according to C standard
those "are always reserved for any use".
Previously, if rc.xml defined only non-default libinput categories,
no default category was created. This meant that configure_libinput()
might totally skip configuring some devices even with default
settings, like tap-to-click.
Fix this by making sure that a default category is always created.
