ServerInfoDialog: Add Server, Connection, and Features tabs
This moves GUI elements into a Glade .ui file.
Server Info is now displayed in three tabs: 'Server', 'Connection', and 'Features'.
The Connection tab shows the connection's security attributes (e.g. TLS version, used ciphers, proxy). This also adds a 'View Certificate' button to that tab.
Additionally, I changed the 'View Certificate' menu item in the account row context menu to 'View Server Info'.
'View Certificate' will be disabled when using a PLAIN connection.
Fixes #6096 (closed).
I'd like to address #9848 in another MR.