JZ: Add basic xlsforms client functions. No tests
Add convenience Client class plus some refactoring
JZ: data, stats & exce tests + some refactoring
JZ: Fetch catalog via dedicated method instead
JZ: Add style test, fix style violations
JZ: Fix #16, #17 and auth by api_token "oversight"
JZ: Restore deleted files, add more forms tests

restore:- `onapie/ona_schema.py` & `tests/unit/test_ona_schema.py`
JZ: Provide requirements files
UK: travis config
UK: add flake8 requirement