file upload handler: message tweak
admin web: link to app version details from app version mgt page
client: maintain availability info, and export via GUI RPC

Maintain the following items:
Per session (i.e. this run of the client):
- active duration (computation enabled)
- GPU active duration (GPU computation enabled)
Total (i.e. since the client first ran here)
- duration (time the client has run)
- active duration (as above)
- GPU duration

Export them in the get_state() RPC; print them in boinccmd.
client: tweak to last commit
client: maintain # of success and failed jobs per project; report in GUI RPC