Various minor improvements to the testing

See merge request lscsoft/bilby!361

fix the emcee writing to file for the prerelease

See merge request lscsoft/bilby!362

Resolve "`InterferometerList.plot_data()` fails for n==3 detectors"

Closes #313

See merge request lscsoft/bilby!363

- Makes the InterferomerList.plot_data() method simply call plot_data on
  each interferometer.

Fix irksome typos

See merge request lscsoft/bilby!356

Convert the frequency_domain_source model to a string in the CBCResult

See merge request lscsoft/bilby!355

Previously, the function was added to the save data dictionary.
Eventually causing the function to be pickled and all CBCResults to be
dependent on bilby. This converts it to a string so that people at least
know which source model was used.

Resolve "Add suggested acknowledgements to the README"

Closes #253

See merge request lscsoft/bilby!352

Fixes "The "create your own time domain source model" example doesn't "work""

Closes #290

See merge request !349

Resolve "bilby-0.3.6 doesn't declare dependency on astropy"

Closes #297

See merge request lscsoft/bilby!351

to make sure the core dependencies are specified properly

Also forces pandas==0.23 to avoid bug

Polychord

See merge request lscsoft/bilby!264

Improve cosmology use

See merge request lscsoft/bilby!271

# Conflicts:
#   CHANGELOG.md
#   bilby/gw/__init__.py

Converts the read_in_result function to a class method

See merge request lscsoft/bilby!345

Improves the load_data_from_cache_file function

See merge request !348

basic checkpointing and resuming

Closes #282

See merge request lscsoft/bilby!346