Historical view of a topic

Specs: https://www.mediawiki.org/wiki/Flow_Portal/Functional_Specifications/History

* Added configurable messages/params per change type
* Added bundling, messages/params also configurable
* Group messages per timespan
* Added some icons: added_*.svg|png & junkdrawer_inverse_*.svg|png
* Applied to both post & topic
* Applied design

Big todos according to spec, but as far as I'm concerned not part of this patch:

* Make the topic & post timestamp only link to history if there are >1 history
  things (I did not yet do this because I don't yet want to query for more data)
* "Actions" per change type (e.g. links "Thanks", "Show changes", ...)
* I'm pretty sure some history stuff currently shows up wrong (I think,
  currently, hiding a post will also show up in topic history)
* Board history page
* We're still missing actions that'll need history, like splitting a topic etc
* Link to historical revision
* History in modal dialogs

Change-Id: I0405498069e6552cada078e079f6ab3bbb920470