Use GLib logging for socket error messages

Use GLib logging for socket error messages

The "perror" logs were not very visible on non-Windows systems
(i.e. the user could see and notice them only when Geany was started
from the command line).
On Windows, those messages were never visible at all.

Add a new debug log message if Geany received an IPC command
from a remote instance.

Also, add a status bar and status window message if the initial socket
creation failed.