Ability to disable autoStop feature using SimpleUser

[DVDripXvid]

Is your feature request related to a problem? Please describe.
autoStop feature is enabled by default and SimpleUser does not gives us the option to disable it.

SIP.js/src/platform/web/session-manager/session-manager.ts

Line 77 in 2e1c525

autoStop: true,

Describe the solution you'd like
An autoStop property on SimpleUserOptions

Describe alternatives you've considered
Disable autoStop feature by default

Probably the extensibility option for SimpleUser would also give us the option to disable it: #1054

Additional context
We also use beforeunload event to do a confirmation thus it might happen that page will actually remain intact. Too bad that autoStop already kicked in.