[FIX] Warning message for pre-bookings

- closes #1338
- warning toggles with success (already contains similar message)
- deleted extra css and instead utilized of messageboxes partial
- vars -> wvars
[ENH] pop up in reject booking is misleading

*closes #1354
[FIX] Wrong icon content code
[IMP] Improved popup messeges in room booking

- closes #1354
[MIN] Small changes on previous commit
[IMP] Mixin to add icons before and after

* Pass icon class name to render icon instead of ASCII code
[MIN] SASSification
[FIX] dates not correctly shown in alarms

- closes #1352