Adds .desktop translations support

It works now the same way as an LXQt app. Although it continues to be an
pure Qt App. There's no LXQt dependency.

There's no need to write a line like this:
	Icon=@CMAKE_INSTALL_PREFIX@/share/pixmaps/obconf-qt.png
The CMAKE_INSTALL_PREFIX isn't necessary, the icon engine will find it.
Fixes the app icon install location

Although LXQt patched QIcon engine search /usr/share/pixmaps, native QIcon
doesn't. obconf-qt is an pure Qt app, so we can't rely on LXQt QIcon.
The proper solution is to install it to hicolor/48x48/apps. That's what's
the hicolor theme is for.
Adds .gitigore