Fix bug rootlogon.C not working under MacOS

Remove ".so" file extensions given to gSystem->Load(). This causes
ROOT to try all valid extensions which for MacOS includes ".dylib".
Suppress warnings in Boost when compiling plot scripts with clang

Tried setting -isystem for Boost, which did not work. Instead
-Wno-unused-parameter is set.
Resurrect plotGui.C

Was still in use.
Move files for mass-dependent fit into separate directory

Move files and adjust build scripts.
Rename "src" directory

Move content of "src" directory to "partialWaveFit" directory. Adapt
build scripts.