It turns out that the resources were mostly not used anyway. Removing
them shrinks LyX binary by ~6MB.
Only autotools have been adapted. cmake will require the same
simplification.
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.
