Expression syntax for rule conditions

[balamg]

Current behavior:
Currently, conditions need to be written in Go code

Expected behavior:

What is the motivation / use case for changing the behavior?
It is much easier to author rule conditions using an expression syntax such as, for example,"$n1.name == 'Bob'" instead of writing Go code for the same

Additional information you deem important (e.g. I need this tomorrow):

[balamg]

Closing this PR as there are significant changes to the expression API in project-flogo/core and this PR is not valid anymore

[balamg]

Re-opening this issue, as this was closed by mistake. (Its associated PR was to be closed)