Add support for the timetracking feature

[xan105]

Since my proof of concept is working better than expected.


It's almost certain the feature will be added to the watchdog process.

And we talked about celes db replacing watchdog %appdata%\AW\steam_cache\data "cache" in #6

• So It would be nice if for an appid there was a playtime: total_in_seconds property to the appid obj. I don't think it'd be easy nor relevant to track time per different source of a same appid. So the property should be per appid and not per appid/source.

• I'd like to request as well a method to easily ask celes to add a given amount of seconds into the playtime total.

[msolefonte]

I need to decide how to store playtime if it is not possible to relate it to any source.

[msolefonte]

Fixed at https://github.com/achievement-watcher/celes/pull/23.