Add data migration feature which will resolve #100
Updated help to include advanced user commands

In regards of leo-project/leofs#103 added help for the update-user-role and update-user-pw commands.
Merge branch 'develop' into feature/manage_prev_and_cur_member
Merge branch 'feature/manage_prev_and_cur_member' of https://github.com/leo-project/leo_manager into feature/manage_prev_and_cur_member