Separate "Create Channel" and "Join Channel" dialogs

[nesium]

Moving this into a new ticket to have a discussion about the issue…

Source: #136 (comment)

Say I have a private room "abc" on the same server where my account is and want to join it.

I click "Add a channel". Should I enter the full address here even though it's the same server? That would differ from the behavior of joining a public room.

So I enter "abc" and click "Create Channel". The web app now tries to find the room "abc" by calling findPublicChannelByName which fails, since the room is private. It then proceeds to call createPublicChannel which creates a new channel with that name but a different identifier.

[nesium]

This is somewhat related to prose-im/prose-pod-system#4, just to bring this back to our attention.