Python's enums are not extensible, values can't be added and they can't
be subclassed. This is problematic if weboob devel adds new values,
because stable weboob will not be able to use them. They would need to
be replaced by a default value or None, which loses information.

Instead, implement custom enums that contain plain constants and support
adding values aftewards.

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.

__str__ is reimplemented in terms of __unicode__ and __repr__ else.

Signed-off-by: Simon Lipp <laiquo@hwold.net>

Signed-off-by: Pierre Mazière <pierre.maziere@gmx.com>

Signed-off-by: Pierre Mazière <pierre.maziere@gmx.com>

Signed-off-by: Pierre Mazière <pierre.maziere@gmx.com>

for web sites providing search and files download

Signed-off-by: Pierre Mazière <pierre.maziere@gmx.com>