Consider making `storage` on the SessionKit to an optional field

[Aaron Cox]

The storage portion of the SessionKit options:

session/src/kit.ts

Line 77 in 9e3995b

 readonly storage: SessionStorage 

Could potentially be made optional to reduce the constructor options required by developers, since a default actually already is being set when building a new SessionKit object:

session/src/kit.ts

Lines 106 to 110 in 9e3995b

 if (options.storage) { 
     this.storage = options.storage 
 } else { 
     this.storage = new BrowserLocalStorage(this.appName.toString()) 
 } 

Unsure of what ramifications this might have, but was suggested in Telegram as something to look into. Without doing any research I think we might be able to do this.