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

Closes #290

See merge request lscsoft/bilby!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 !264

Improve cosmology use

See merge request !271

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

Converts the read_in_result function to a class method

See merge request !345

Improves the load_data_from_cache_file function

See merge request !348

basic checkpointing and resuming

Closes #282

See merge request !346

Utils upgrade

Closes #153

See merge request !298

# Conflicts:
#   CHANGELOG.md

- Parameterise by the simpler start_time rather than a trigger time
- Uses the lal functions to read in the lines of the cache file
- Promote warning messages to raised errors if the data is not
  succesfully loaded
- Add doctsings

Resolve "Consistency of constants between bilby and lalsuite"

Closes #224

See merge request !343

Add slack workspace, update the summary info, and add conda forge badge

See merge request !342