What type of PR is this?

Add one of the following kinds:

• enhancement/feature

What this PR does / why we need it:

• It grants uniform schemas to share code with Notification compliance #53 on webrtc-events API.
  • It uses VvoipSessionInformation for request responses and possible async notifications.
  • Internal code to parse and handle voice-video session info can be shared
• Simplify internal classes removing redundant schemas
• Improve work to include implicit notifications for Allow implicit subscription for RACM and CallHandling #55

Which issue(s) this PR fixes:

Fixes #54 - SessionStatus is the new schema that will be used for notificiations, that includes VvoipSessionInformation the common data structure for a voice-video session used for all WebRTC APIs

Special notes for reviewers:

The previous examples are maintained, in order to grant compatibility with previous version 0.1.2.
Check changelog input to identify changes on schemas

Compare previous version here: version 0.1.2
With purposed MR version here: version 0.1.3

Changelog input

## BYON CallHandling v0.1.3 
 
### Added 
 
- `VvoipSessionInformation` expanded to include all fields used related to a 
  single voice-video session 
- `SessionNotification` to include any posible notification, expanding the 
  VvoipSessionInformation schema 
 
### Changed 
 
- `SessionInvitationNotification` and `SessionStatusNotification` are now handle 
  inside `SessionNotification`. 
- `SessionNotification` is just a wrapper for `VvoipSessionInformation` so 
  it can be used on next stages for implicit event susbcriptions. 
- The schema is not changed on structure, so interoperability is granted with 
  previous 0.1.2 version. 
 
### Fixed 
 
- Descriptions and relevant information for all sections 
   
### Removed 
 
- `SessionInvitationNotification` - Became part of `SessionNotification` 
- `SessionStatusNotification` - Became part of `SessionNotification` 

Additional documentation

No extra documents, improved API inline descriptions