Update strings in po files

[jonbrett]

The current strings in the translation .po files are from the shell extension (from which this applet was forked).

Whilst most, if not all, of the strings currently used in the applet match those in the .po files, the comments about where the string was generated don't make sense (extension.js doesn't even exist!).

The .po files should be re-generated from the current applet source and any strings that have already been translated can be copied across.

I remembered this when merging #9

[nitso]

Sorry for that commit spam :)

[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.