Refs #7178. Add a test for existing log properties.

Though http://www.mantidproject.org/Run#ISIS_Muon_data does have
a list of run properties read from the Muon files, it wasn't checked
in any of tests before.
Refs #7178. Update test to check for new properties.
Refs #7178. Improve test robustness against type mismatch.
Refs #7178. Make names of new parameters better.
Refs #7178. Add code to read new properties from Nexus file.
Refs #7178. Do a minor refactoring.

Instead of going through a huge pain of calculating average of time
series manually (from a string!) we can just use an appropriate
method.
Refs #7178. Change property not found/set messages.

It is not an error when expected log is not found or set.
Refs #7178. Use ostringstream to build info string.

Concatenating strings is inefficient and tedious.
Refs #7178. Add code to display new properties.
Merge remote-tracking branch 'origin/feature/7178_muon_temp_and_field_logs'