VE-1306: Fix by replacing hardcoded names of types

mwBlockImage -> wikiaBlockImage
mwInlineImage -> wikiaInlineImage

Comments in the methods are not updated because this change is meant to be reconsidered later on (but it takes us where we want to be in the short term).
Merge pull request #4051 from Wikia/VE-1306

VE-1306: Fix by replacing hardcoded names of types