Rename gangType

[Snorre98]

I feel it is unclear what "gangType" is, so I would suggest renaming gangType to "department".
So this issue would just make it more clear that GangType (would be Department) is not Gang, but is a parent of Gang.

This way we would have:

Department -> Gang -> Section

I dont think we represent Section yet, but might want to. This is unrelated to the issue.

Where Department instance would be "Driftende", with some Gang(s):
"MG", "KSG".

Another Department would be "Kunstneriske", with some Gang(s):
"SIT", "Pirum"

gangType might be refered to in a variation of ways in frontend so a good start for solving this would be to see where the endpoints which fetches gangTypes is used and rename the related values there.