Hot fixes for maintenance and robustness

This PR proposes several fixes to ease the installation and add a little more robustness to the otbox.py code.

By default when a repo is checked out, otswtoload.json points to the latest develop branch
The installation script removes the old version of the software for a clean install
Added stdout and stderr logging
Enclose picturetoscreen handling code in try-except and add a fallback when the picture url cannot be retrieved (used to cause crashes)

openwsn-berkeley / opentestbed