Migrate int to bigint

[juliusknorr]

Seems we still have integer columns which especially for file_id in large instances can easily be exceeded.

We should add a migration to fix this:

ALTER TABLE `oc_files_lock` 
	CHANGE `id` `id` BIGINT(20) unsigned NOT NULL AUTO_INCREMENT,
	CHANGE `file_id` `file_id` BIGINT(20) unsigned NOT NULL
	;