Move flow( 'setupEditForm' ) to base/action.js

* Renamed all this.(post|topic|header) vars to this.object (more generic, for
  easier inheritance)
* Moved chaining-based flow( 'setupEditForm' ) to base/action.js, where code has
  been split up in different functions, allowing for inheritance & easier
  overriding
* Instead of usins lots of jQuery functionality to build HTML, it's now a string
  of HTML (similar to PHP templating)
* There was some duplicate code in setupEditForm; now removed
* Made setupPreview & hidePreview return this, to allow chaining
* Showing/hiding of form/content is now done in CSS, based on
  new .flow-edit-form-active class on container
* Renamed html node classes to more generic name (not including type)
* Instead of passing initialContent literals everywhere, generalized that into 1
  function

That's probably about it

Change-Id: I1adfcd9bc6e1c48e07cf223b7ce63e03fc4668bc
Merge "Move flow( 'setupEditForm' ) to base/action.js"