Method get_page_data should be a member of Experiment instead of ContentCore

[jobrachem]

This would allow access with the same shortcut from elements and sections.

[jobrachem]

In alfred3 v2.0, the following methods/properties allow data access:

• alfred3.experiment.ExperimentSession.session_data: Dictionary of full data
• alfred3.experiment.ExperimentSession.values: Dictionary of all input elements
• alfred3.experiment.ExperimentSession.metadata: Dictionary of metada
• alfred3.experiment.ExperimentSession.client_data: Dictionary of client information
• alfred3.experiment.ExperimentSession.move_history: Dictionary of movement history
• alfred3.experiment.ExperimentSession.get_page_data(): Dictionary of a page's data
• alfred3.experiment.ExperimentSession.get_section_data(): Dictionary of a section's data