Datatype is not preserved for overridden property values

[vijaynalawade]

Current behavior (how does the issue manifest):
When app property value is overridden using ENV or JSON mechanism, type casting is not performed. Due to this, app property of type integer can be set to string value and vice-versa.
Expected behavior:
Type casting must be performed to ensure type safety.

Minimal steps to reproduce the problem (not required if feature enhancement):
Set app property of type int and print its value using Log activity. Now, override value with string value. The Log activity will print string value.
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.x
Additional information you deem important (e.g. issue happens only occasionally):