Implemented new search relevance ranking algorithm

[devos50]

Fixes #2250

[devos50]

@lfdversluis can you review? I will fix the import order error in the pylint after your review. Also, I think it's hard to reduce the number of local variables in the search_in_local_torrents_db methods (I'm not even sure how pylint counts them since my count results in a lower amount).

[lfdversluis]

Import order, was noted but just so you don't forget

[lfdversluis]

Comments given, Windows 64 bit is failing too.

[devos50]

Traceback (most recent call last):
  File "C:\Python27\lib\threading.py", line 763, in run
    self.__target(*self.__args, **self.__kwargs)
  File "C:\workspace\jenkins\workspace\GH_Tribler_PR_tests_win64\tribler\Tribler\Core\Utilities\twisted_thread.py", line 55, in _reactor_runner
    reactor.run(installSignalHandlers=False)
  File "C:\Python27\lib\site-packages\twisted\internet\base.py", line 1194, in run
    self.mainLoop()
  File "C:\Python27\lib\site-packages\twisted\internet\base.py", line 1203, in mainLoop
    self.runUntilCurrent()
--- <exception caught here> ---
  File "C:\Python27\lib\site-packages\twisted\internet\base.py", line 825, in runUntilCurrent
    call.func(*call.args, **call.kw)
  File "C:\workspace\jenkins\workspace\GH_Tribler_PR_tests_win64\tribler\Tribler\Core\APIImplementation\threadpoolmanager.py", line 50, in caller
    fun(*args, **kwargs)
  File "C:\workspace\jenkins\workspace\GH_Tribler_PR_tests_win64\tribler\Tribler\Core\Libtorrent\LibtorrentMgr.py", line 482, in do_dht_check
    lt_session = self.get_session()
  File "C:\workspace\jenkins\workspace\GH_Tribler_PR_tests_win64\tribler\Tribler\Core\Libtorrent\LibtorrentMgr.py", line 186, in get_session
    if hops not in self.ltsessions:
exceptions.TypeError: argument of type 'NoneType' is not iterable

[devos50]

retest this please

[devos50]

@lfdversluis thanks for the review. I don't think the algorithm is perfect right now and it might need some minor tweaking but for now, I think it is ok for a first version of the GUI.

[devos50]

@whirm ready for your review

[whirm]

@devos50 is @synctext happy with the new algo?

[devos50]

@whirm I will discuss it with him tomorrow.

[whirm]

Ok, let me know about it

[whirm]

Needs a rebase

[devos50]

@synctext forgot to ask, can this be merged?

[devos50]

Let's see how this algorithm works out. Any improvements to the algorithm can be made later 👍