This allows to make whole-day events.

Python 3.4 added new Enum types that enforce a value belonging to the
enumeration.
This commit retires our homemade enum and use Python's Enum type.
Python 2 compatibility is achieved with "enum34" package.

Housing and Calendar capabilities are updated to use those new enums.

[calendar] add timezone parameter to calendarevent in order order do get the good date/hours in ical exports

[boobcoming] improve ical export, Make sure to use '\r\n' to end lines rather than just \n (RFC 2445 4.1)

python modernize.py --no-six -f libmodernize.fixes.fix_print -w

With manual fixes as the import was put always on top.

refs #803

- split attends command in two (attends / unattends)
- use formatter in export command