Don't installing conflicting mime type for *.*64

There is already an mime type for Nintendo64 roms called application/x-n64-rom.
This one has to be extended instead of installing a conflicting type. Otherwise
only one of the desktop entries for mupen64plus-ui-console or m64py works and
not both.
Allow QSpinBox lower than 0

As of the config option merge in glide64mk2 we have to be able to set sub zero values as well in order to support the new game ini default
Merge pull request #14 from V1del/negativeQspinBox

Allow QSpinBox lower than 0
Merge pull request #7 from fayvel/mime

Don't installing conflicting mime type for *.*64
Merge pull request #16 from fayvel/deprecated

Replace some deprecated python constructs + Fix PyQt elements search paths
Replace deprecated pyqtSignature with modern @pyqtSlot decorator