coerce.ToType should support all go primitive types

[masterclock]

Current behavior (how does the issue manifest):
only a subset of primitive types are supported, especially, not including uint* types
Expected behavior:
support uint,int8,uint8,int16,uint16,uint32,uint64 etc
Minimal steps to reproduce the problem (not required if feature enhancement):

Please tell us about your environment (Operating system, docker version, browser & web ui version, etc):

Flogo version (CLI & contrib/lib. If unknown, leave empty or state unknown): 0.X.X
0.9.2
Additional information you deem important (e.g. issue happens only occasionally):