flogo webui: build and target shim triggers

[mellistibco]

I'm submitting a ... (check one with "x")

[] bug report => search github for a similar issue or PR before submitting
[x] feature request
[] support request
[] general question

Expected behavior:
A build option to target a shim build. If a shim trigger is used within the app, a shim build option should be available. The build dialog should ask the user to select the shim trigger they wish to target for the build.

Minimal steps to reproduce the problem (not required if feature enhancement):

What is the motivation / use case for changing the behavior?

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

Additional information you deem important (e.g. issue happens only occasionally):