Check consistency of ParserOutput and re-parse if necessary, refs 3395

[mwjames]

This PR is made in reference to: #3395

This PR addresses or contains:

• As outlined in MW 1.32+, MCR breaks move tests #3395, this follows as regression introduced by MCR
• We can try to cover up the issue by comparing the ParserOutput content we retrieve an see if it is consistent and in case it is not re-parse the entire content of the page (which is costly and I'd like to avoid that)
• How do we know it fixes the issue? because all tests pass again!! [0]

This PR includes:

• Tests (unit/integration)
• CI build passed

Fixes #3395

[0] https://travis-ci.org/SemanticMediaWiki/SemanticMediaWiki/jobs/423572872

[mwjames]

Can be merged (as measure to prevent inconsistent data) BUT we keep it for now to see if any other unforeseen changes to the ParserOutput (due to MCR) will create undetected issues.

[kghbln]

I have added this one to 3.1.0, however it may be brought forward to 3.0.x if there is the need to do so.