Inventory plugin for renewing tokens

• Added new inventory plugin to auto-renew access token for Aruba Central
• Added a sample inventory source file (aka inventory plugin config file)
• Modified Readme and other documentation explaining the use of this inventory plugin

Changed Inventory Variable

Changed inventory variable from ansible_httpapi_session_key to ansible_httpapi_central_access_token to resolve conflict with ansible.netcommon collection

Fixes and documentation updates

Bug fixes in the module files related to Python3
Added requirements.yml to install ansible.netcommon for Ansible 2.10+

Initial Release 0.1.0

Updated plugin

Python 3 compatiblity