Fix the display of Device Types to show all device types used in a project

[LDalby]

I noticed that the Device Types tab on the project front page only lists one type (for the DK case), but when I look at Deployments they list a second type. Should this be possible? I expected the Device Types to show all types used with in the project.

[annavik]

Nice catch!

I looked into this and the device "UKCEH Trap" does not belong to any project. If a device is deleted from project, I think we should also remove it from project deployments. I suspect this could be a problem also for other entity types.

Suggestion on fixes:

• When joining entities on backend (for example deployment device), make sure entities belong to project (this would fix this issue)
• When an entity is deleted from project, delete connections to other entities (this would prevent this issue)
• When an entity is deleted from project, actually delete it from database (this will eliminate entities without connections lingering around after delete, but it would also make delete action tricky to revert if needed)

Assigning you @mihow since this is all backend, let me know what you think about the fix suggestions :)