added defaultBranch to Branches type, changed ui-bundler version for better testing experience in intellij, corrected fetchBranch functionality, wrote reducer for single branch and unit tests

scm-ui-components/packages/ui-types/src/Branches.js

@@ -4,5 +4,6 @@ import type {Links} from "./hal";
 export type Branch = {
   name: string,
   revision: string,
+  defaultBranch?: boolean,
   _links: Links
 }