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.

Use Z instead of z in the timestamp format

Don't use put_time() because it’s not in gcc 4.9, in shitty-debian “stable”

Use strftime instead

Do not fail e2e if the database cannot be removed because it's not there

Add missing algorithm include

Add missing ctime include

Update changelog with the history thingy

[skip ci]

Send the muc history when a second (or more) resource joins a room

Document the sending of the muc history

If the maxHistoryLength is negative, make it 0

Instead of doing a broken SQL request that returns weird lines

Index the owner for the global conf table

Only save the logs if recordHistory global config option is true

Delete the database before each e2e test, to start fresh

Move get_first_non_empty to louloulibs/utils

Only save messages coming from real MUC participants in the database

Not messages coming from the room, for example

Default max_history_length is 20, not 0

When joining a channel, send the most recent history found in the database

When saving the logs, the date must be in seconds, not nanoseconds

Add a global configure ad-hoc command, with max history length

Add get_first_non_empty and use it into Database to simplify a little bit