Added language button to bottom bar.

Tapping the button downloads list of languages for article and
present these in a table view for selection.

Removed no longer needed header references.

Added "Test Wiki" entry to languages json file.

Added languagecount, lastmodified, lastmodifiedby, redirected and
needsRefresh properties to core data article entity.

Fixed bug which causes subsequent section to not be downloaded if
operation for doing so was interrupted.

Article entity flag “needsRefresh” now allows any article entity to
be marked for re-sync with server data (after edit, or soon perhaps
a pull to refresh etc). Does so in non-destructive manner - i.e.
existing history or saved items don’t get orphaned or removed.

Fixed bug which could cause duplicate history items on edit.

Fix for crash on rotate with initial install before any article loaded.

Fix for possible crash on web view scroll when TOC onscreen.

Fix for weird black bar behind web view occasionally on rotate.

Fix for enumeration / mutation search results crash.

Fix for white which appeared above or below web view when scrolled
beyond top or bottom edge of article content.

Change-Id: Ie07416d25a627cb71a30cabf79240550cae02212