Improvement: New connection management

This is just to track development and notes as I go along. Not for merging.

- [x] Remove network forms
- [x] Auto generate nice connection names 
- [x] Remove predefined connections from database
- [x] Remove "channels" from Core::add_connection() and edit_connection()
- [x] Handle SSL error message
- [x] Add server password support
- [x] Consider removing convos chat and just go to the last network conversation instead. The reason is that it's very confusing when you /close the last conversation