This patch introduces IPC::Connection which becomes the new base class
of ClientConnection and ServerConnection. Most of the functionality
has been hoisted up to the base class since almost all of it is useful
on both sides.
This gives us the ability to send synchronous messages in both
directions, which is needed for the WebContent server process.
Unlike other servers, WebContent does not mind blocking on a response
from its client.
Step one of moving DesktopServices::open handling out of process. This
makes it easier to do things like read in associations for which program
opens which files or protocols. This gives users the ability to modify
the associations without having to rebuild :^)
