Apply the system monospace font to log messages

Monitor the monospace-font-name key from gsettings-desktop-schemas and
update the font if it changes.
Fix duplicate child warning for detail view
Factor out timestamp handling

Add gl_util_timestamp_to_display() and move microseconds-to-string
handling to it.
Add timestamp to kernel events list view
Add timestamp to security events view
Add timestamp to commandline events view
Add timestamp to system events view
Increase window width and height request

https://bugzilla.gnome.org/show_bug.cgi?id=710397
Make event view timestamps slightly smaller