Handle olsr neighbors who silently go away (UI)

Make sure that neighbors who go away silently
are actually removed from the links list.
Be more careful about lingering olsrd processes

Killall oslrd processes before attempting to
start a new one in OlsrdControl.start().
Update JsonInfo users to handle IOExceptions

This means that we can stop the OlsrInfoThread
after a few successive incomplete connection
attempts.
Use an Iterator for concurrent modification

Unless we use an Iterator to move through
clients array, we cannot remove items
during the loop.