Add support for Siri Shortcuts

[eopo]

The iOS App could receive support for Siri Shortcuts and offer Actions for the user to perform and use in their scripts.

The following actions are on the top of my mind:

• Get reverse alias:
  Input: Alias address, Target Addres
  Returns: Reverse Alias
  Throws Error: if the wanted alias address does not exist (Or auto-create it, but throw if that is not possible)
  Usecase: Automatically send E-Mails from within a shortcut without exposing the real address
• Create custom alias:
  Input: Alias address
  Returns: Alias address
  Throws Error: If the wanted alias cannot be created
  Usecase: Automatically generate an alias adress for further use in shortcut, where the custom part could be defined by prior shortcut actions.
• Create random alias:
  Input: Domain (Optional)
  Returns: The alias address
  Throws Error: If no alias can be created (E.g. if the domain is not available anymore or the user exceeded their quota
  Usecase: Automatically generate an alias address for further use in shortcut
• Get aliases:
  Input: A search term (Optional)
  Returns: A list of existing aliasses, filtered by a search term if one was set
  Throws Error: Hopefully never
  Usecase: Let the user choose from a list of aliasses, e.g. in preperation for the "generate reverse alias" action.