Adds the ability for the drag and drop file upload to handle subdirectories. You drag and drop and it doesn't kill your sub-folder substructure. Nothing more, nothing less.

Be aware that the frontend AND backend required changes. i.e. be aware of your browser cache when testing. I uses an incognito window.

# Manual tests

* Open a repo
* optionally go to a sub-directory
* Select File upload
* Drag and drop a folder with files and sub-folders like
```
test_git/
├── 1
│ └── 2
│ ├── test2.txt
│ └── test.txt
└── test.txt
```
* optionally select an additional directory for "create directory"
* Commit changed
* Check if the files are now in the repo according their full paths and file names, taking into account the optional "create directory" parameter