Adding functionality to connect mne rt-client to fieldtrip rt-client.

This addresses https://github.com/mne-tools/mne-python/issues/982 but is still at an early stage. There are some problems still and it is not straightforward to do the testing yet. As of now, I have modified the original C code by @LauriParkkonen to add the capability for emulating from a file. The compiled binary (64-bit, CentOS) in this folder http://neuro.hut.fi/~mainak/neuromag2ft-2.0.0.zip should hopefully work good as the server. Something like this worked on my machine:

`$ neuromag2ft-2.0.0/bin/x86_64-pc-linux-gnu/neuromag2ft --file mne-python/examples/MNE-sample-data/MEG/sample/sample_audvis_raw.fif`

However, I haven't been able to get the whole pipeline working yet. Anyway, I'll fix it soon and notify. I am adding TODOs below to keep a check-list of what needs to be done + questions.

TODO
[] Fix docstrings in code by S. Klanke to comply MNE-Python conventions

Questions
[] Since the `MneFtClient` code is so similar to `MockRtClient`, maybe combine them into one with an additional argument?
[] How should the symbolic constants be handled? Right now, it's a blind copy from S. Klanke's code with only PEP8 fixed.

cc @LauriParkkonen @mluessi @Eric89GXL @agramfort