Added NROER E-Book data entry script and other minor changes

**NROER E-Book data entry script done**:
- Script processes CSV file to get the data in the application.
- All the resources are uploaded with their ```url``` field.
- For each new folder *File* gsystem page is created with the name of ```base_folder``` column.
  - This page will hold the collection of pages under it.
  - If *.zip* folder has cover page then relation ```has_cover_page``` is getting created.
  - ```content_org``` of this page will have cover page image.
  - Resource available in this page is ```.zip``` of all the pages.
- *Prerequisites* to run this script:
  - Should have CSV files (```nroer_biology_ebook.csv```, ```nroer_maths_ebook.csv```, ..., etc).
  - Should have ```nroer_ebook``` folder under home (```~/nroer_ebook```) containing data in ```.zip``` format.

**Other changes**:
- Previously in ```nroer_data_entry.py``` file ```save_file()``` was written in the same file. Which is removed and calling ```save_file()``` from ```file.py``` file.
- Commented *shelf* part in ```file.py``` and ```page.py```.
- Minor errors in ```sync_existing_documents.py``` and ```filldb.py``` are handled.
- ```has_cover_page``` relation has been added in the ```factory.py``` file.
- Now by passing ```count``` and ```first_object``` as a *kwargs* we could prevent default collection making behavior in ```save_file()```.
- Removed error causing script from ```collection_ajax_view.html``` file.

<hr/>

**After taking this pull please run the following script:**
```python manage.py filldb```