Morpher pluggable transport: Select algorithm for packet size morphing

This is a ticket to resolve a) of comment:1:ticket:4680 :

We should evaluate whether the final morpher transport should use 'random sampling', or 'morphing matrices' to select a packet's final packet size.

In 'random sampling', you have a packet size probability distribution of a target protocol, and you pick a random variable, and then you shape your packet to be of that size. By 'morphing matrices', I mean the technique described in the paper Traffic Morphing: An efficient defense against statistical traffic analysis which attempts to minimize the padding overhead imposed by packet size shaping.

Since our morpher transport will try to turn Tor traffic into HTTPS traffic, as far as packet sizes are concerned, we should evaluate whether the 'morphing matrices' method is worth it. We can build a tool that uses both methods on a couple thousand packets, and see which method is more effective. If 'morphing matrices' is indeed more effective, we should see whether it's effective enough to justify its troublesome implementation.

I stupidly attached all relevant files to #4680 (moved), but let's continue the discussion here to avoid flooding #4680 (moved) more.