Re-implement log viewer

* Logs get huge, so just tail them
* Point at correct location for aqd log
Remove reset functionality

It is far too dangerous in a production system for now.
We should restore it with much more safety checking at some point.
Re-implement disk space accounting

* Use du instead of re-inventing the wheel, this also catches files in sub-directories.
* Switch to a more useful list of locations to monitor.
* Ignore free space.
Remove reset trigger

Trigger condition is bogus for a production system.
Check if warehouse exists before checking it's status
Re-implement DaemonTool class

Replace the DaemonTool class with something we can use to monitor services controlled
by init scripts, which is what we would expect in a production environment.
Add sandbox information page

This uses an external script to give details of sandbox status.
It also restores the about (credits) page which got removed earlier.