wlfreerdp: reorganize source files, add input methods

We split the one massive source file into multiple separate
source files and headers, just like it is done for other
clients.

We add a new "wlfInput" interface which will try to
initialize mouse and keyboard at startup. Mouse inputs
already work, keyboard inputs need further investigation.

Signed-off-by: Manuel Bachmann <tarnyko@tarnyko.net>