Deleting entity record

[rgonek]

• [x] Display more info about deleting entity
• [x] Display form for delete options
• [x] Logic for cascade delete
• [x] Logic for set to null

Available delete options:

• nothing
• set null
• cascade delete
• ask user

[rgonek]

Deleting now works very well, but still need some work.

• [ ] Optimization (use WHERE ProductId IN (...))
• [ ] For cascade delete we need check what to do with sub entities in deeper levels, now we do cascade delete for every sub entity