Quassel IRC

For the mono client, we need to make the connection dialog more intuitive for users not familiar with Quassel's core/client concept. Seele's review as well as many user questions have proved that the current way of providing the standard core connect dlg and an additional "Use internal core" button are confusing.

For the mono client only, I would suggest offering a direct way to connect to IRC, either by selecting an existing network/identity, or, if none exists, a quick way of creating those (say, enter a server address and a nickname, and then create a default network/identity from that; possibly popup the standard config dialogs).

We could still offer using a remote core by a button "Connect to remote Quassel Core" or something; but that should be clearly visible as an advanced thing rather than the default action to do.