Adapted 'book single room' page

* Refactored BookingConfirm RH
* Splitted common elements in booking pages in several widget templates
* Refactored clientside validation
* Rendered repeatability/flexible days with WTForms
* Fixed holidays warning
* Fixed rendering glitch in RB calendar for single room
* Removed old template
* Added callback to timerange widget
* Minor style tweaks
Post-WIP fixes
Cleaned util JS functions

* Removed unused datetime validation
* Added go_to_room helper
Validation for reservation with days in advance
Applied info-helper class
Fixed PeriodWidget template for 3-step reservation
Room selector widget improvements

* Fixed clear filter deselecting rooms
* Prevent submit form on ENTER
* Avoid sending selected rooms twice in the form
* Fixed leaked variable
Timerange widget now handles TAB inputs properly
Missing semicolons and similar JS stuff
Fix Book/Prebook button in room details
Avoid global JS vars
Some python/import optimizations
Fix flexible days validation for daily booking
Make BR state enum picklable

otherwise db log pickling fails
Fix ugly text in rb map widget
Post-rebase fixes
Removing some unused code
Migration: is_cancelled instead of is_sent...
RB HTTP API w/ new DB (no booking creation yet)
Remove unused import