Add options that change how the editor in an activity is displayed

[Dagefoerde]

Together with the HS Hannover and Synergy Learning, we are planning to contribute the following enhancement to the activity configuration:

• configure how the document will be opened - a dropdown - (Globally configurable for default setting):
  • Embed - Current window
  • Embed - New tab
• by default, the embedding iframe uses the maximum size available within the given theme layout. we add settings to override the size:
  • Width - text input of the iframe for the OnlyOffice document server editing interface
  • Height - text input of the iframe for the OnlyOffice document server editing interface
• Checkboxes to determine whether activity name and description are displayed on top of the editor (unchecked by default to leave more space for the editor)

(This is one of the tasks resulting from the general idea that I presented in #5.)

[logicexpertise]

Looking forward to your PRs for the proposed features