Group csv import view ignores invalid ids and just assign new ids

[Ignas Mikalajūnas]

Group CSV import view will ignore your ids if they are invalid (start with @ or + for example) instead of giving you an error, which can cause a lot of problems when importing huge lists of groups with ids that you care a bout (like ids that must match ids in an SQL database)

We don't want our users to silently get 10 groups with mangled ids, it is better to notify them of such errors, and allow users to fix them. So if there is an invalid ID we should point it out in the error message, and not change it to whatever we think is good.