Add functionality to replay cellular traces

[BobAnkh]

Ref:

• Mahimahi Paper and Mahimahi Repo
• CellReplay

[BobAnkh]

Note that we have to comprehensively integrate the inner model of CellReplay. Though I haven't read its code, if it mimics the behavior of cellular channels, it will emulate bi-directional paths. While emulating both paths inside a single shell in mahimahi is a desired design, we may have to have the ability to break it into two cells, as our client-to-server and server-to-client paths may go through different cells.