Decipher Performance Enhancement

Removed unnecessary code duplication in Decipherer.cs
Added a loop breakout when all three functions have been determined.
Rearranged the code so that operations is determined once and applied to
each encrypted signature instead. This should greatly improve the
performance of the decipher as it won't have to run though all the loops
each time to decrypt a video/url.
Renamed some variables and comments to clear up some of the trial fix I
made.
Removed test code from previous commit
Tidied up Decipher method

Moved duplicated code into a method, loop breakout added if all three
cipher methods are found.
From previous commit, restored original DownloadURLResolver.cs as the
methods need to remain the same.
Merge pull request #75 from Cyano/master

Improved the performance in the Decipher