Support adding custom apps to the page context

[nailor]

Example:

Site has a frontpage, controlled through the CMS. However, the user wants to add a news ticker to the page (separate app). At the moment would mean site specific coding to the RiskiCMS internals.

Provide an option to specify special handlers somewhere (for example in the settings-file):

PAGE_HANDLERS = {
  '__root': {
    'news': 'somenewsapp.views.ticker',
  }
}

This would pass a context instance named news to the template of the __root page containing what ever the somenewsapp.views.ticker returns.