[BUGFIX] fixed minor bugfixes

- bugfix when adding account-contact without position
- bugfix operations on list in account-contacts / activities when nothing is selected
- bugfix in error message when deleting account with more than 3 contacts associated


__Tasks:__

- [x] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | none
| Fixed tickets |  https://github.com/massiveart/POOL-ALPIN/issues/65 https://github.com/massiveart/POOL-ALPIN/issues/66
| Doc           | none