implement synthsForUMap

returns only one synth per server
make synthsForUMap customizable in FreeUDef
FreeUdef can now use UMaps
introduce allowedModes for UMapDef

normal UMapDefs are only allowed on \sync and \normal args, but
FuncUMapDefs and ValueUMapDefs also work for \init args. This can be
altered per UMapDef.
allow UMaps for PointSpec
add two UMapDefs for points

intended use is for PointSpec