Migrate groups to proper unique id

[Altonss]

The following points a required for a migration to unique ids for groups:

• Edit the LoyaltyCardDbGroups table to contain a new ID column that's an integer.
• Edit the LoyaltyCardDbIdsGroups table to refer to the group ID instead of group name.
• Migrate all current memberships to the new setup.

@TheLastProject thinks, the easiest way is to just create 2 temporary tables and then create the new stuff like it has been done at newVersion 10 in the DBHelper class.

Originally posted by @TheLastProject in #669 (comment)

These steps are needed, because the current situation is blocking for a good implementation of #669 for example.

[Altonss]

Should the group names still all be distinct? For the moment it is not possible to create 2 "Test" groups, should this limitation remain?
By the way, @TheLastProject you could assign me to the issue, I'm currently working on it.

[TheLastProject]

Should the group names still all be distinct? For the moment it is not possible to create 2 "Test" groups, should this limitation remain?

I think that makes sense, I don't really see any benefit for users to make 2 groups with the exact same name after all.

By the way, @TheLastProject you could assign me to the issue, I'm currently working on it.

Thanks for picking this up! :)