Remove ConfigService checking for Python and Matlab executable names

[Martyn Gigg]

The ConfigService behaves slightly differently if the executable name is Python or Matlab. At the time this was due to the fact that we needed to know where the Mantid bin directory was if running in a standalone interpeter in a different directory.

Now that we have the MANTIDPATH variable this behaviour should be changed so that Mantid is consistent regardless of the executable name.

The change will mean that when the ConfigService starts it looks for the Mantid.properties file in the following way:

(a) If MANTIDPATH is defined then use this path, else (b) use the executable directory.

[Martyn Gigg]

(In [8826]) Removed check for the executable name from the ConfigService. It now either uses the path pointed to by MANTIDPATH or the executable's directory if the former is not set. Also renamed a couple of functions relating to this so that it is clearer what their return values point. Re #2256

[Russell Taylor]

(In [8832]) Trickery no longer needed now that Mantid is consistent in where it looks for properties files. Re #2256.

[Peter Peterson]

(In [8855]) Fix to help vanilla python. Refs #2256.

[Stuart Campbell]

This ticket has been transferred to github issue ​3103