Gaffer startup : Add signals compatibity shim
Gaffer startup : Add signals compatibity shim

This makes the Signals classes available from the main Gaffer namespace as before.

johnhaddon/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,hradec/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,hradec/gaffer,andrewkaufman/gaffer,hradec/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,hradec/gaffer,GafferHQ/gaffer,GafferHQ/gaffer,GafferHQ/gaffer,hradec/gaffer