Show list of accounts in a window

Create a new window where we can list all configured accounts. All
accounts are listed as root objects in an outline view. The idea is that
it will be possible to navigate folders and other types hierarchical
data structures from it, although that is functionality which will have
to be added later.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Use tls property instead of local variable

We set the default port number based on if TLS is enabled or not. This
should refer to the property that we set earlier, not to the temporary
variable which was used to do it.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Make account name customizable

Each account should have a name appropriate for display. As default we
use username@hostname, but the user might want to customize this. Add a
name key to the account dictionary and fall back to the default if it's
not defined.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>