Add the following functions, which existing code to use
`pandas.DataFrame` objects:

 - `integrate_fft`: Integrate a bandwidth around a target frequency in
   DStat FFT results.
 - `dstat_to_fft_frame`: Compute FFT for set of DStat measurements.
 - `dstat_to_frame`: Convert DStat text file results to
   `pandas.DataFrame`.
 - `reduce_dstat_data`: Reduce measurements for multiple DStat
   experiments to a single row per experiment with an aggregate signal
   value.

See function docstrings for more details.

Add `get_experment_data` method to 0MQ API, which returns a
`pandas.DataFrame` containing two columns, `time_s` and `current_amps`
which correspond to the *time in seconds* since the start of the DStat
experiment, and the measured current in *amps*, respectively.

Support for new 0MQ plugin controller



See merge request !8

Fix bugs (minor typos)

Fix bugs (minor typos)

Prior to this merge:

 - Incorrect UUID was being stored in completed list.
 - `save_text` was being called in the `save_plot` 0MQ API method.

As of this commit, both of these issues are fixed.

See merge request !7

Separated plot save dialogue from actual saving.