Improve flexibility and robustness of Acoustics Module

[jmcvey3]

There are three main changes in this pull request:

1. Added the option to determine the number of datapoints in each FFT when creating the sound pressure PSDs. This was currently hardcoded to the maximum FFT length, i.e. the total number of datapoints in each window, which might be more resolution and require more storage space than desired
2. Changed names of bin and windowing related attributes on the PSDs to make them easier to understand
3. Gain was improperly added - the sign has been corrected

Minor changes are refactoring some of the argument type checks to clean them up.

[jmcvey3]

Looks like some remaining dependency issues related to timestamps

[akeeste]

Thanks @jmcvey3! Just two small suggestions on the use of _check_numeric

[akeeste]

Add call to _check_numeric in place of the removed error check

Suggested change

	_check_numeric(fn, "fn")
	_check_numeric(fmax, "fmax")

[akeeste]

We should only check that the values are numeric if they exist. If the values are given then the type is not checked:

Suggested change

	if not hasattr(pressure, "sensitivity"):
	_check_numeric(pressure.sensitivity, "pressure.sensitivity")
	if not hasattr(pressure, "fs"):
	_check_numeric(pressure.fs, "pressure.fs")
	if hasattr(pressure, "sensitivity"):
	_check_numeric(pressure.sensitivity, "pressure.sensitivity")
	else
	raise TypeError("'pressure.sensitivity' not provided.")
	if hasattr(pressure, "fs"):
	_check_numeric(pressure.fs, "pressure.fs")
	else
	raise TypeError("'pressure.fs' not provided.")