Build properties

Here it is !

The underlying wiring is done: process -> data -> db.

I don't have data endpoint yet, it should make the subject of another PR I believe, That one is already big enough ...
Shall we have a id key which is hash(buildid, name) ? so that we can update the property directly?

http://dev.mysql.com/doc/refman/5.6/en/insert-on-duplicate.html