Add better error message for files which exceeds $wgMaxImageArea

Add better error message for files which exceeds $wgMaxImageArea

Added a TransformTooBigImageAreaError to allow setting an extra message.
Added also size-*pixel messages to show the value of $wgMaxImageArea
with some formatting.

This error is still throwing for all files, to fix bug T34387 this needs
a follow up with a proper check. I am not sure, if a File::isLocal() is
okay, because files from a DBForeignRepo maybe transformed on the same
server, so the check needs to be done also for this. For APIForeignRepo
the check is done on the foreign server.

Change-Id: Ieba12e424c8bddb1961a30d3f9ea5c8ff241abb5