Most of these tests fail because they rely on the old set_data method,
or try to set attributes that aren't settable.

The tupak.core.prior call in the core/__init__.py file was accidently
removed during testing. This puts it back in.

- Adds in comments from Denyz, and general tidy up.
- Closes #83

Also fixes a typo

Set total data loaded for the PSD calculation from frame file to be `psd_duration`

See merge request Monash/tupak!75

Also adds documentation for buffer_time

- Removes overwrite_psd
- Make the data actually be set

- Add explicit sampling_frequency, duration, and start_time
- Generalise the 1s offset to an argument, buffer_time

In particular, merge bb9b5904 changes to set_data into their new
location.

add KAGRA

See merge request Monash/tupak!70

Add two extra seconds of data when reading from frame

See merge request Monash/tupak!73

Adds a set method from an array - this is used by set_data and
inject_signal.

Rather than passing around a list of interferometers, have a defined
set. Motivation: in several places we had dangerous calls to
interferometers[0].attribute which will get confusing if not all IFO's
have the same duration etc. This enforces that they do.

start_time -> epoch

Ensures that a useful error message is reported when the data is not set

Burst

See merge request Monash/tupak!71