The timer code used to trigger periodic statistics message sending used
ITTI. Together with a high frequency reporting (e.g. 1ms), this resulted
in high CPU usage. This commit reimplements this:
* using a thread that is synchronized to the RU (if there is no MAC, we
  assume there is no RU generating a tick so we create the tick source
  ourselves)
* no RB trees but plain arrays
* smaller interface for users
* slight user interface changes
* remove stopped timer state: such timer might be simply removed
* remove one-shot timers

* only set up timer for sending requests
* simplify interface for timer setup
* on timer expiry, do not pass through stats request function but
  directly send the reply
* Remove whatever report structure and use stats request directly for
  inferring the data to send

For whatever reason most of the files had their permission
changed from 644 to 755, which is not wanted.

Fixed bug related to the reporting of timing advance to the controller that severely dropped the performance of the remote scheduler

Signed-off-by: Xenofon Foukas <x.foukas@sms.ed.ac.uk>

Signed-off-by: Xenofon Foukas <x.foukas@sms.ed.ac.uk>