Fix #204 - add support for XHTML

Together with colors-xhtml in the candy-plugins repository (branch
feature/xhtml-colors) this will enable Candy to show validated
XHTML if enabled with the `enableXHTML` config flag.

In order to make this work, I had to fix the muc plugin of strophe.
Until strophe/strophejs-plugins#14 is not merged, this is done manually.
Remove unneeded comment
Make XHTML parsing more robust & display error in case there is one
Fix XHTML parsing in text

- Escape textNode html tags (they're not allowed there)
- Remove margin from p-Tags in messages (native clients tend to use it
  and it crashes the layout a bit)
- Escape submitted text before sending it
Revert escaping on submit (instead escape in plugin)
Merge dev
Merge branch 'dev' into feature/xhtml-colors
Update version
Fix Action: add IDs everywhere

Fixes #217. This is a cherry-pick from the refactoring branch.
fix #216: rename view.resources to view.assets
Fix #220 invalid html tags generated

Because the createHtml used previously the XMLGenerator
of Strophe, it assumed <br> to be a real tag (<br></br>),
therefore it didn't work out.

Switched now to some jQuery stuff (not beautiful but it works).
Merge dev
Fix #219: don't act on non-room disco replies

Related: #207
Fix #215: on before/after events, use same evtData

In case there's a need for other hooks, please
open a new issue or reopen #215.
Fix copyright header
Fix #214: improve events to be canceable

- Add new canceable event `candy:view.room.before-add`
- Add new canceable event `candy:view.private-room.before-open`
- Make `candy:view.message.before-send` canceable
- Make `candy:view.message.before-show` canceable
Add sourcemap to candy.min

Might help with debugging.
Merge dev
Improve #214: prevent errors in certain cases when false is returned
Merge branch 'dev' into feature/xhtml-colors