Release 0.99.3
Drop use of deprecated dbus.glib

When writing Python apps that will use asynchronous DBus calls and
signals, python-dbus must be initialised with the appropriate main
loop.

sugar currently does this by importing the datastore module from
sugar-toolkit-gtk3, and the datastore module uses the deprecated
and confusing dbus.glib module (which automatically and non-obviously
sets the default GLib main context as the DBus mainloop).

Eliminate the dbus.glib usage from sugar-toolkit-gtk3 as part
of the effort to make sugar initialised the DBus mainloop in a
more explicit and non-deprecated fashion.
Ensure entity value is type str

There are times when the entity value passed in for substitution
is of type unicode. This causes Rsvg to fail when processing the
SVG. This patch checks for unicode and converts it to utf-8.

Fixes #4621
Commit from Sugar Labs: Translation System by user cjl.: 40 of 40 messages translated (0 fuzzy).
Fix translations in non standard prefix

This drops a lot of code at the same time. The code in
__init__ was:

* Using a SUGAR_PREFIX environment variable that is not
defined anywhere
* Hardcoding prefix to /usr
* Setting up the sugar-base domain which doesn't exist anymore

The i18n module code was overcomplex because it was thought
for language packs which we don't support anymore, it was
not handling correctly locales with a country prefix, it
was hard coding the python prefix and it was not sorting
the directories as it intended too anyway.

The logic is very simple now. Use the locale directory in
the same prefix sugar-toolkit-gtk3 was installed, unless
SUGAR_LOCALEDIR is defined (for self contained bundles).
Fix translations domains to point to new toolkit
Update .gitignore