Hide the back button on the first page

https://bugzilla.gnome.org/show_bug.cgi?id=702106
Updated Spanish translation
update Punjabi Translation
keyboard: Fix compile warnings
account: Fix compile warnings
location: Adjust padding
location: Fix a deprecated call
Update egg-list-box
account-page: Fix compilation error
Update for egg-list-box changes
page: Use notify_by_pspec
center-container: Fix get_preferred_width
assistant: Relabel buttons

"Previous" is the standard label for going back a page in an
assistant.
Updated Polish translation
Updated Lithuanian translation
summary: Make the button keyboard navigable

Although the button is keyboard activatable through the mnemonic,
since those are not shown by default, users might miss it and have no
other way to activate it using only the keyboard.

https://bugzilla.gnome.org/show_bug.cgi?id=702397
keyboard: Unconditionally create the localed proxy

We always need the localed proxy since we read the system default
input sources from it.

https://bugzilla.gnome.org/show_bug.cgi?id=702399
Update egg-list-box
Updated Marathi Localizations
Assamese translation updated