Demisto-py

Fixed an issue where the attribute mapping for the `search_incidents` model was incorrectly looking for `incidents` not `data`.

* Fixed the `filter` parameter in `search_incidents` method to be required as specified in the API.

* Fixed a bug in the `import_layout` method where an API endpoint was not working as planned.

* Added `import_playbook` method for importing a playbook to Demisto.
* Added `import_script` method for importing a script to Demisto.
* Added `import_incident_fields` method for importing an incident field to Demisto.
* Added `import_incident_types_handler` method for importing an incident type to Demisto.
* Added `import_widget` method for import a widget to Demisto.
* Added `import_dashboard` method for import a dashboard to Demisto.
* Added `import_classifier` method for importing a classifier to Demisto.
* Added `import_layout` method for importing a layout to Demisto.

* Enabled host and path parameters to function with trailing or leading slashes.

* Improved error message when missing authentication parameters.