Enhancement: append to clipboard plugin

[sdaau]

I was rather frustrated by the lack of a clipboard manager that can "append" to clipboard (as often I have to select words across text, and build sentences out of them) - I just recently learned about Glipper, which is thankfully in Python - and has a plugin architecture :)

So this is my append to have a "append" functionality - basically, when plugin is started, a menu entry appears, saying "Appending: False". When you click on it, it changes to "Appending:True" - in this case, whenever you press Ctrl-C, the copied content will be added at the end of the 'previous' (or 'current', depending on how you think of it) history entry, separated by '\n'. To get out of this mode, just click on the "Appending:True" menu entry again - note that you'll have to click the first entry of the clipboard history afterwords, to access the appended/merged content so you can paste it.

Hope this can be useful to users,
Cheers!