Make it possible to re-create missing SourceChange events

This change add the flag fillGaps for the createSccs and createScss
endpoints. With this flag you can re-create missing events. Traversing
from the root of the commit tree every missing event is re-created
until the specified commit or tip of the specified branch is reached.

Solves: Jira GER-1545
Change-Id: I2c3d5067c0e080b04c8890ceff18b4f6534ec274
4 files changed
tree: a2aa01d1a717a5e5d408a7c4b0059e54df4f6d65
  1. src/
  2. BUILD
  3. external_plugin_deps.bzl