Make measures search path smaller

[tammojan]

I think the current list of directories being searched is too large. This could lead to confusion if multiple instances of measures data are installed.

I propose a small refactor, where only to paths are searched:

• A custom path, set in .casarc
• A default path, set at compile time (cmake -DCASADATA=...)

To acommodate for a directory relative to casaroot, we could accept some syntax within the pathnames, for example %CASAROOT% and %CASAHOME% in both the custom and default path.