Limit data to specific time interval. More efficient averaging.

* I added a 'gen.trim' key to the diag_param dict.
** Its purpose is to allow for trimming the data to a specific interval.
** This allows averaging shots whose breakdown time may have changed
** either due to adding a splitter in the circuit or some other variables.

* Made the averaging routine more efficient by using np.mean and
** taking advantage of the .values() function in a dict.
use trim.lower.limit and a range instead of low.limit and high.limit
Generalized plotting of bands to vectors

I had to make some structural changes in order to plot bands around vector
diagnostics.

* plt.fill_between has been moved to vme_2d_plot_scalar_signal
* introduced an extra_signals as a parameter in my plotting functions.
	By default, extra_signals has either value '' or ['', '', ''].
	When I want to plot a band, I send the appropriate information
	using the extra_signal parameter.
* Updated vme_get_sig_min_and_max to take in a signals_list which is
	a list of dicts.  Each dict corresponds to a vector component and
	a scalar is a list containing a single dict.
* Updated vme_get_extra_from_data to always return a list whether the
	component is a vector or a scalar.

Remember: extra_signals is a list of components which are in turn arrays
	values as a function of time.
	extra_signals[min/max][component][time]
fixed bug where not having bands on vector diagnostic is a problem
changed smooth_win to fix breakdown time inaccuracies with 5kV plasmas
updated and cleaned up code a little
Plot bands around avg magnetic signal from hall sensors

This problem is non-trivial because the transformation from Hall
Voltage to actual magnetic field is a non-diagonal matrix.  The result
is that the matrix does not necessarily commute with the averaging
operator.

I completely rewrote my plot_hall_for_shots routine.  Big changes:

* User input must be of form [['847', '848'], ['899']]
* User may no longer just enter ['847'] and must enter [['847']]
* Plot hall for shots now converts each shot's hall voltage to magnetic
* field BEFORE averaging the value of the magnetic field.
cleaned up get_b_from_hall
cleaned up code and fixed sensor parameter with plot_hall
added hall.b parameters for plotting purposes