Move Framework dependent build options in main CMakeLists file

In its old place it only worked when set by the command line. If not set
then the Framework sub-directory didn't see the flag and didn't create
the Remote/RemoteAlgorithms targets meaning that MantidPlot was linking
to a non-existant library.
Refs #7355
Merge branch 'feature/7355_remote_jobs_on' into develop