Added device installation and deletion methods

[aerjenn]

This PR adds some extra functions to the notification hub python package in order to also be able to create device installations in Notfication Hub, so this can be done from a Python back-end as well.

Functions added :

• add_device_installation(registration_data)
• get_all_device_registrations()
• get_device_registration(registrationid)
• get_device_installation(installationId)
• delete_device_registrations(registrationId)
• delete_device_installation(installationId)