Massively upgrade symposion

* Remove markitup (to be replaced with Ace editor)
* Use DUA decorators
* Removed custom signup bits
* Upgraded dependencies
* Added migrations
* Namespaced template locations
* Removed html5parser/sanitizer (for now) - parsing functionality
should be moved out entirely to a hooks
* Replaced ProposalScoreExpression object with a function that returns
F() expressions