Impliment Quit function

[l300lvl]

I thought this might be easy to impliment but alas I am still not experienced enough, at any rate some of the code from this commit seems very similair, and perhaps they used your work and built upon it, either way it should be easy enough to impliment, hopefully in the indicator and in the messagetray

https://github.com/linuxmint/Cinnamon/commit/315c00291fe7d04cb3fb3cca8d3a0e883e65a88f