Include icon.png in root dir of applet

[jonbrett]

The current applet icon will only display correctly in CInnamon's applet settings form if the user already has installed hamster (since it uses the hamster-time-tracker icon).

This means that users browsing the applets via Cinnamon settings and who don't already have hamster installed will get the "default applet" icon.

This can be addressed by including a icon.png file in the root dir of the the applet

[elbenfreund]

As this Issue documents the cinnamon applet is now maintained by the Mint Linux team.
As such this repository is kept around for historical and migration reasons.
Contributors are encouraged to head over there and no work will be done on this
repository at all.
Thanks for your support.