1586 fix booking days limit

Limit choice of days in 3-step booking
 - Add new bar to the calendar to show days where booking is not possible.
 - Replace error report with nicer message.
 - Extend the Bar class to accept a room id directly upon instantiation
   (as a keyword argument)
 - fixes #1586
 - remove unused sass rule for bar borders
 - remove rule for IE version prior to IE9
 - remove unused import