Uploading Text Using TEI-XML File (WIP)

[kvchitrapu]

1. added cli.py sub-command
2. moved create_new_text() and add_document() from gretil.py to a generic module data_utils.py

Test:

1. Download TEI-XML file from Isavasyopanishad
2. `python scripts/cli.py publish-text --title "isa" --slug "isa" --tei-path /tmp/ambuda.org_proofing_isavasyopanishad-text-only_download_xml.xml
3. 

[kvchitrapu]

@akprasad , I updated with staging url. Let's try to catch up on db update when you have time.