more unit tests and corresponding refactoring (#174)

src/git-source-settings.ts

@@ -0,0 +1,12 @@
+export interface IGitSourceSettings {
+  repositoryPath: string
+  repositoryOwner: string
+  repositoryName: string
+  ref: string
+  commit: string
+  clean: boolean
+  fetchDepth: number
+  lfs: boolean
+  authToken: string
+  persistCredentials: boolean
+}