make install doesn't install all ressources

[umlaeute]

after a successfull compilation, I do a make install which installs the following files:

/usr/local/bin/iannix
/usr/local/share/applications/iannix.desktop
/usr/share/pixmaps/iannix.png

This misses any files searched by the binary, e.g. Museo.ttf is not installed anywhere (it should probably be installed to /usr/local/share/iannix (see #22)

Also, currently this installs the iannix.png into /usr/, whereas the rest installs to /usr/local/.
Instead, the PREFIX variable should be used throughout.

[dvzrv]

I used PREFIX="/usr" qmake-qt5 && make && make INSTALL_ROOT="${pgkdir}" install on Arch Linux to get around the issue with the install destination.