Correctly process the situation when squashfs file isn't there
Made error message more verbose (as suggested by Clem)
Select default timezone based on IP address

Closes #25
Added option for automatic login

The user configuration screen now has a checkbox for autologin.
If checked, post installation sed scripts are run, covering all
the most used display managers.

Closes #18
Get current xkb layout more reliably
Query GeoIP City database for time zone as well
Parse xkb rules only once using xml.etree.ElementTree
Slightly more concise assign_keyboard_* callbacks
Defer keyboard preview generation for smoother scrolling
Merge pull request #37 from kernc/autologin

Added option for automatic login
Merge pull request #39 from kernc/default_timezone

Select default timezone based on IP address
Merge pull request #42 from kernc/kbd_switch_delay

Annoying delay when switching keyboard layout
Merge pull request #31 from monsta/patch-4

Correctly process the situation when squashfs file isn't there
Grammar & style of i18n labels

Mostly very minor grammar and/or consistency fixes in
translatable labels, full sentences in help labels, etc.
Two label asignments are replaced with GTK+ stock items which
results in correct translations, standard mnemonics, optional
button icons, ... These two are `GO_FORWARD` and `APPLY`. The
latter replaces "Install" on the installation overview screen.