Before the ContentHandler merge, using action=edit&appendtext=... on a
non-existent page would treat the page as if it existed but had no
content. After the merge, it throws an error incorrectly claiming that
appending is not supported for wikitext.
The fix is to create a new, empty content object when appending and
there is no existing content.
Change-Id: I61f2cf3911a7d9d8553fc3f745e545cb1bcfd270
Cleaned up EditPage, removing and fixing comments etc.
The most prominent changes are:
* improved handing for parse errors
* improved handling for image redirects
* better readability because one huge try/catch block was removed
Change-Id: Ie33720922eb05dda89a22ca1f5f0cba4b1d31129
