Make incognito image a resource

https://bugzilla.gnome.org/show_bug.cgi?id=696078
Use a custom style for incognito mode

https://bugzilla.gnome.org/show_bug.cgi?id=696078
Generate .gitignore with git.mk

Keeps it up to date. Also, allows cleaning Autotools-generated files
with 'make maintainer-clean'

https://bugzilla.gnome.org/show_bug.cgi?id=720548
Reset the language setting when all languages are removed from the UI

https://bugzilla.gnome.org/show_bug.cgi?id=720896
Make alt + left/right navigate back/forward

https://bugzilla.gnome.org/show_bug.cgi?id=720897
Updated Greek translation of help
about-handler: Align correctly the about page of incognito mode in RTL

https://bugzilla.gnome.org/show_bug.cgi?id=721363