refactor: move manager-specific code under lib/manager (#1573)

lib/manager/bazel/index.js

lib/manager/docker/index.js

lib/manager/index.js

lib/manager/meteor/index.js

lib/manager/meteor/update.js

lib/manager/node/index.js

lib/manager/npm/extract.js

lib/manager/npm/index.js

lib/manager/npm/update.js

lib/manager/resolve.js

lib/workers/dep-type/index.js

lib/workers/package-file/index.js

lib/workers/repository/index.js

lib/workers/repository/updates/determine.js

test/manager/index.spec.js

test/manager/meteor/update.spec.js

test/manager/npm/extract.spec.js

test/manager/npm/update.spec.js

test/manager/resolve.spec.js

test/workers/package-file/index.spec.js