Allow setting conversation password on conversation creation via API

[mario]

Currently to set a password on room creation you need two API calls:

• create a conversation
• set a password

I'd like an optional password field on the creation flow to avoid the extra network call

[nickvergessen]

Same for the invites. I guess it is time for an api/v2/ at least on the creation flow it could be improved a lot.

[nickvergessen]

It would basically be nice to have this for all kind of features/settings we have.
So I wonder how we can make this scale without having 20 parameters on the API method.