Update and refactor festival datatype

[giplt]

Here's a number of suggestions to improve the festival datatype:

• Refactor festival module to new pagetype coding style Converge to one coding style for datatypes #135 Convert festival to new datatype style #337
• Add 'about'-field to show in the festival default view, preferably by making use of the existing mechanisms for the datatype webpage, i.e. rich content trough wymeditor, revisions, translations
• Add 'excerpt'-field to show on top in lineup and timetable views
• Add location, time and tags to festival module contributions: On signing up participants can currently say which days they intend to join. It would be helpful for building the timetable if in stead they would enter their preferred location(s), day(s) and add at least one tag for a theme that fits their contribution.
• Make page configurable through a web interface: A workable first approach could be a simple textarea containing the current xml. Slightly better would be multiple textareas for separate chunks of information in the settings xml. Of course the best would be dropdown menus, checkboxes etcetera for noobs to set up a festival. However that could be done in a next iteration, considering also Refactor datatype festival #133.
• Add translations: Relatively easy would be adding support for multilingual contributions (perhaps reusing what is currently in place for the datatype webpage). A bit trickier is the translation of email templates that may need filling in certain fields. This should ideally make use of the translation/dictionary support. Possibly we should make all translations editable through a separate settings page and add messages (also from festival) there?

[matthijskooijman]

On signing up participants can currently say which days they intend to join. It would be helpful for building the timetable if in stead they would enter their preferred location(s), day(s) and add at least one tag for a theme that fits their contribution.

I think these would be separate features (that can co-exist): The former "what days to join" was intended to know how much participants to expect (i.e. how much lunch to arrange), while the latter "info about a contribution" would be intended to help create the timetable.

A bit trickier is the translation of email templates that may need filling in certain fields.

In #337, I've moved the e-mail content from the page XML to be translated strings, which means they're trivial to translate, but no longer customizable at all. This might need some more work to allow both translating and customization...

Possibly we should make all translations editable through a separate settings page and add messages (also from festival) there?

Yeah, this thought has also occurred to me, maybe this is something to be implemented now, then...

[matthijskooijman]

Add 'about'-field to show in the festival default view, preferably by making use of the existing mechanisms for the datatype webpage, i.e. rich content trough wymeditor, revisions, translations
Add 'excerpt'-field to show on top in lineup and timetable views
Add translations:

These are partly covered by #341, though editing and revisions for the about and excerpt fields is not supported yet.