FileUploader first commit.

Collects files, renames them upon size and age constraints, tests the above.

Lots of ```TODO(dkorolev)```. And time to discuss export events in more detail.
This mutex and while(true) in ExporterThread look too complex. May be use std::future and std::async ? And export thread will run while(scan_shows_that_no_more_files_left_unsent) ?

http://stackoverflow.com/a/17204246