Single file collections (#132)

* Files based collections skeleton

* listing file based cards

* create new entry with collection

* moved lookupEntry to main backend

* Editing single page Collections file

* List widget basic implementation

* Adjustments for test-repo

* check if value exists before trying to iterate over

src/constants/collectionTypes.js

@@ -0,0 +1,2 @@
+export const FILES = 'file_based_collection';
+export const FOLDER = 'folder_based_collection';