Refactor buildSrc into an independent project.
Refactor buildSrc into an independent project.

- New independent build project, called build-plugin
- Sub module kit-release will be released into public and it will
  allow 3rd party kit developers to use it.
- Sub module weaving is for fabric internal build toolings.

Change-Id: I63d4332531746915e65941d661dd185c2e160dd6

dejavu1988/digits-android,rameshvoltella/digits-android,metao1/digits-android,jaydeep17/digits-android,twitter/digits-android,dejavu1988/digits-android,jaydeep17/digits-android,metao1/digits-android,twitter/digits-android,jnbt/digits-android,rameshvoltella/digits-android