Add "Close Other Documents" to documentcontextmenu

I find this very practical, and as the documentcontextmenu isn't
exactly crowded yet ...
new translation strings
fr
Merge pull request #1 from philmassart/traduction

Traduction
move parser to read, it will also be used run-time
wip create translatable strings file
more robust
Merge remote-tracking branch 'upstream/master'
Merge pull request #281 from philmassart/traduction

French translation (with new strings)
Merge pull request #279 from uliska/close-documents

Add "Close Other Documents" to documentcontextmenu
fix document context menu close other when called on a different document that the current one
make separate python files to harvest strings from

this gives some feedback about which help page is being translated.
much simpler
Merge pull request #282 from mamoch/master

First implementation of midi input
Merge remote-tracking branch 'upstream/master'
add lineno attribute to parser
wip create pot directly from md files
fix & in filenames
Merge branch 'master' of github.com:wbsoft/frescobaldi
md2pot basically working