User password regular expression should be taken from configuration.

[Audrunas]

Because users module is stand-alone, it cannot inject to cms.config, so it should be done after #634 will be done.

Also, a message (globalization key) should be saved to the settings also (e.g. message should explaint, thar password must contain at least one number, at least one letter and be at least of 8 symbols length)