Added Host Add page and test 

Hosts page class
* Added _configuration_button_locator, _add_new_host_locator, _remove_host_locator to Hosts class
* Added @add_button property, @remove_button property to Hosts class
* Added click_add_new_host() method to Hosts class
* Added does_host_exist() method to Hosts class
* Added check_host_and_refresh() method to Hosts class
* Added click_remove_host() method to Hosts class

Add subpage
* Added new Add page for Hosts subpages

test_infrastructure_provider_pages.py
* Added new test test_host_add() to test_infrastructure_provider_pages.py
* Added new test test_host_delete() to test_infrastructure_provider_pages.py
* Added new single_host_data fixture to test_infrastructure_provider_pages.py

Page base class
* Added _wait_for_invisible_element to Page class

Template data
* Added template data