Autocomplete branch names in `arc feature`

Summary: SPOOKY

Test Plan: `arc feature <tab>`

Reviewers: cpojer, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7376
Provide ConfigurationManager to LintEngine in Arcanist

Summary: Unbreaks ArcanistSingleLintEngine / ArcanistScriptAndRegexLinter from recent config churn.

Test Plan: `arc lint --engine ArcanistSingleLintEngine --rev HEAD^`

Reviewers: btrahan

Reviewed By: btrahan

CC: csilvers, aran

Differential Revision: https://secure.phabricator.com/D7377
Merge branch 'master' of http://github.com/facebook/arcanist