Author: Petr Škoda
MDL-34441 add maintenance mode to db migration and improve lang strings
http://git.moodle.org/gw?p=moodle.git;a=commit;h=6ceaf9807c68c67b14e26cda98eb541979b49bd5
http://github.com/moodle/moodle/commit/6ceaf9807c68c67b14e26cda98eb541979b49bd5
+ 2.4 en [climigrationnotice,tool_dbtransfer]
+ 2.4 en [dbtransfer,tool_dbtransfer]
+ 2.4 en [enablemaintenance,tool_dbtransfer]
+ 2.4 en [enablemaintenance_help,tool_dbtransfer]
+ 2.4 en [options,tool_dbtransfer]
+ 2.4 en [targetdatabase,tool_dbtransfer]
+ 2.4 en [transferdbintro,tool_dbtransfer]