This patch has security level related changes for torbutton.
Migrated 'security level' related strings from torbutton.dtd to new
securityLevel.properties file, loaded by JS in the new securitylevel
component in Tor Browser. Removed the old Security Slider xul and menu
entry in the torbutton menu. Also 'fixed' the german (de) torbutton.dtd
file (was valid listing of XML entities, but it broke my dtd parser used
to migrate strings)

Added new "extensions.torbutton.inserted_security_level" pref to
torbutton that piggy backs off the existing
"extensions.torbutton.inserted_button" pref logic. Toolbars are reset to
the Tor Browser default when the new 'inserted_security_level' pref is
false. Coupled with the changes in tor-browser, users which upgrade will
have their toolbars reset to the new design.

After the browser has been updated, notify the user by displaying
a message on the about:tor page. Also, in release and alpha builds,
include on the about:tor page below the Tor Browser version a link
to a simplified changelog page (which continues to be located at
about:tbupdate).

Remove strings that were used for the "New Circuit Display" promotional
banner which previously was shown on the about:tbupdate page.

This reverts commit c93f06417e0bdbd6d709ec5109938347d1d38123.

We include Torbutton directly into the browser on Android. The features
.xpi we bundle is not used.

Patch idea by sysrqb@torproject.org.

Version bump and CHANGELOG update

Add "Downloading update" property string.