Fix the datetime parsing to handle optional fractions of seconds

fix #3266

Remove two sneaky log_debug

Refactoring louloulibs and cmake

Use OBJECT libraries
Remove the louloulibs directory
Write FOUND variables in the cache

Actually, just use the C locale for the date formats

We don’t need any UTF-8 support here, and it’s more portable

Only use the C.UTF-8 LANG value

In time.cpp, use the en_US.UTF-8 locale, instead of en_US.utf-8

(which apparently doesn’t work on freebsd)

Conditionally use strptime if we don’t have std::get_time

Parse the timezone myself, instead of using the broken strptime

See

https://lab.louiz.org/louiz/biboumi/issues/3215
https://github.com/andikleen/glibc/blob/master/time/strptime_l.c#L746-L747

for why strptime() sucks

We use std::get_time now, to parse the date and time. And we parse the
timezone by hand.

fix #3215

Fix parse_datetime by always using a 'z' as the timezone

Because some plateform accept Z and z, but some only accept z…

Fix the parse_datetime by using %Z instead of %z

If anybody knows why fedora accepts both, but it only works with %z on
debian, please tell me.

Add parse_datetime

Fix to_string(time_t) and write a unit test for it

Respond to MAM requests on a channel JID

At the moment, result-set-management is not implemented, the whole history
(well, at most 1024 messages) is returned.