Renamed the two gtid-classes to better match MariaDB documentation. One
domain-server-sequence-combination is now a "Gtid", as these identify
a transaction. A "GtidList" contains a list of Gtid:s for handling multi-domain
server variables composed of multiple comma separated Gtid:s.
Removed unused methods and renamed some existing ones. Moved the Gtid-code
to its own file.
'mysqlmon' is still accepted but 'mariadbmon' is loaded instead.
This is done at runtime instead of e.g. by using a symbolic link,
so that a warning can be logged.
The warning is logged and the translation of the module name is
made by the code that loads the modules so that it's easy to do
the same thing for other modules as well.
In a subsequent commit the documentation is updated.
