Update Makefile

Add a new 'help' recipe to the Makefile. Make this recipe the default. This
recipe lists out all available recipes and gives a brief description of their
effects.

Add a new 'test-docstrings' recipe to the Makefile. This recipe calls
`testimony`, just as Travis does right now.

Update the `.PHONY` special target. Wrap the line so as to be readable on
narrower editors.

Add comments to the makefile to visually separate its sections.
Make .travis.yml less special

Remove the `testimony validate_docstring ...` commands from `.travis.yml`.
Instead, make Travis call a functionally equivalent command in the Makefile.

Do not install any Python packages directly from `.travis.yml`. Instead, update
`requirements-optional.txt` and make travis install the modules listed therein.
some fixes for the org test cases
Merge pull request #930 from kbidarkar/fix-org-tests-jun26

some fixes for the org test cases
Merge pull request #931 from Ichimonji10/refactor-tooling

Refactor tooling
Update readme file

The Makefile was recently updated with new recipes. Update the readme to reflect
those changes.
Merge pull request #933 from Ichimonji10/readme

Update readme file
Update API host tests

Now to create a host medium_id is required. The tests was updated to
create a host with the extra required field.
Merge pull request #935 from elyezer/api-host-test

Update API host tests
Add get_fields method to orm.Entity
Add class `Model` to module `robottelo.entities`

This new class represents a "Model" entity in the Satellite application. For
reference material, see `apidoc/v2/models` on a Satellite deployment.
Merge pull request #934 from Ichimonji10/entities

Add class `Model` to module `robottelo.entities`
Merge pull request #925 from elyezer/orm-get-fields

Add get_fields method to orm.Entity
Implement orm.OneToManyField