File upload stats

[defnax]

• Added mutex, orginal work by @RetroPooh file upload stats (lib) #107
  updated code to latest Master

Cyril wanted save feature someone need to implement this

Another problem is that you're not saving the upload stats. So they are lost accross restarts, which somewhat kills the entire idea since upload stats are supposed to be long-term stats. But ftServer does not have a saving system.

All accounted for, it seems that it would make much more sense to store them with p3FileDatabase in ft_database.cfg.
That means:

• add to p3FileDatabase class the functions to update the upload stats, as called from ftServer (no mutex needed in ftServer for that since the one is p3FileDatabase will be used)
• create a new RsItem in rsfilelistitems.h to store the upload stats.
• add the proper lines to load/save these stats in p3FileDatabase::loadList() and saveList() using these created items