Fix invalid MIME type

Desktop entry contains invalid MIME type (imaqe/x-xpixrnap) which should
be imaqe/x-xpixmap.

Signed-off-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
Fix Category in desktop file

Desktop entry contains the Hawaii value for the Categories entry but it
should really be X-Hawaii since it's a custom value.

Signed-off-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
Use a generic icon, until a custom one is available

Signed-off-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>