[IMP] Store CSRF token in session

generated when needed, reset when user changes
[IMP] Require CSRF token for JSON-RPC calls
[IMP] CSRF token in cookie-based API requests
[DOC] Document cookieauth changes
[IMP] Add config option for CSRF checks
[IMP] Add optional referer check for POST

fixes #1238
[FIX] 'Go Back' link pointing to Timetable view now

- Closes #975.
[IMP] New design of contribution navigation bar

* Added icons witch links pointing to timetable and conference list
* Change all <table> tags to <div>
* Closes #975
[FIX] Restore 'go back' in navigation bar
[FIX] Missing CSRF checks
[IMP] OrderedDict available in Python 2.6

 * using `ordereddict` library;