Change sampled parameters

See merge request Monash/tupak!31

# Conflicts:
#   tupak/sampler.py

changed random seed to avoid multi-modal posteriors.  Added comments to tutorial so user can understand each step

- If no saved data exists when loading, a valueerror is now raises. This
  catched that exception to work as expected.

- Adds a filename option for direct loading
- Raise an error if no information given

# Conflicts:
#   tupak/__init__.py
#   tupak/result.py
#   tupak/sampler.py

Moritz Huebner: Made sampler.result a property and moved some of the stuff that happens in run_sampler in there.

# Conflicts:
#	tupak/__init__.py

Merge branch 'change_sampled_parameters' of git.ligo.org:Monash/tupak into change_sampled_parameters

# Conflicts:
#   tupak/__init__.py

If DISPLAY environ not found, then default to the Agg matplotlib
backend. Useful for running on clusters etc.