build on extension/test launch

[jpoon]

Request for comment cc: @johnfn @rebornix

Force a build via gulp on extension launch/test. I tend to forget to run gulp watch manually; often times I would change the source, run it, and wonder why the behaviour didn't change before the duh moment.

With this change,

• Pro: Guaranteed that the TS is compiled; no need to run gulp watch or npm compile manually and check console if things compiled correctly. auto-runs tslint.
• Con: Adds build time (5s right now) before you can launch the extension/run tests

[rebornix]

LGTM. I put the check in pre-commit but definitely this change is necessary.