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".
Move font_texture_create() to font.c so it can be used for purposes other
than rendering the menu, for example server side decoration.
Refactor menu.c and menu.h to use this more generic font_texture_create()