Validation - no check on form creation

[PascalinDe]

currently, it is possible to create an empty form (no titles, no subjects, ...)

• make the English title mandatory see also Internalisation - forms are not correctly displayed in list of forms #309
• make at least one option mandatory

[PascalinDe]

the problem is that the check checks that MainTitle is set and a string, and the data that gets passed is:

'{"en":"","fr":"","de":""}'

so the check passes, but no actual data is passed

[PascalinDe]

#313 fixes broken test on form title - however as far as I can see in the code the subjects should not be empty either and this is still broken, I'll add a separate PR for that