gproject: Make toolbar buttons insensitive when no files displayed

This hopefully avoids some confusion regarding what the +/- mean
GeanyLaTeX: Replace NZV-makro with EMPTY-makro
Addons: Replace NZV-makro with EMPTY-makro
GeanyVC: Replace NZV-makro with EMPTY-makro
Treebrowser: Replace NZV-makro with EMPTY-makro
Spellcheck: Replace NZV-makro with EMPTY-makro
GeanyDoc: Replace NZV-makro with EMPTY-makro
GProject: Replace NZV-makro with EMPTY-makro
GeanyVC: Replace NZV-makro with EMPTY-makro
GeanyLaTeX: Replace NZV-makro with EMPTY-makro
Merge pull request #110 from frlan/generell/replace_NZV

Replacement of NZV-makro #2
Addons: Compilefix
codenav: Adding Federico Reghenzani as new maintainer for codenav plugin.
Removed default keybinding
updated Changelog and README
Merge pull request #132 from shankhs/master

Removed default keybinding
Update of German translation
Geanylua: fix leaks
Update of Copyright comment on German translation
Update of po files for string freeze of Geany-Plugins 1.24