Resolve "Release v1.3.0"

[1.3.0] - 2021-07-20

Added

• Add (un)subscription request
• Add explicit get method
• Register a service worker (if available) that manages update messages
• Automatically open a WebSocket connection if ServiceWorker is not available
• Disconnect the WebSocket when closing the connection to the database
• Add a getter for openedCollections in Session
• Add multiple handlers per object

Changed

• Use NotificationHandler to notify the app when an update arrives
• Automatic subscription when opening a collection
• Change key type of waitingPull from DeltaCRDT to CObjectUId
• Remove implicit get when performing onRead
• Remove the limit of frequency of get requests
• Open an already opened object in a different mode raises an exception

Closes #62 (closed)