correct constraints for trajectory and point UMapDefs
add link_point UMapDef

using the new ULink system. Example:

UChain('sine', [ 'pulse', [ 'u_o_ar_0_bus', 1.0 ] ], [
'wfsDynamicPoint', [ 'point', 'random_trajectory', 'quality', 'better'
] ], [ 'wfsDynamicPoint', [ 'point', [ 'scale_point', [ 'point', [
'link_point', [ 'url', "2/point" ] ], 'move', [ 'circle_trajectory', [
'speed', 0.4, 'radius', Point(1, 1) ] ] ] ], 'quality', 'better',
'u_i_ar_0_bus', 1, 'u_i_kr_0_bus', 2, 'u_i_kr_1_bus', 3 ] ]).gui