src/SIP.js: remove '.js' from require paths
Let modules require() their own dependencies:

- LoggerFactory requires Logger
- Session requires Session/DTMF
- WebRTC requires WebRTC/MediaHandler and WebRTC/MediaStreamManager
- Dialogs requires Dialog/RequestSender

see https://github.com/joseph-onsip/SIP.js/commit/67f7128382bda905d646f617733b50ca5d88b8ea
More dependency cleanup:

- Transport module depends on WebSocket, not window
- LoggerFactory module depends on window.console, not window
- Hacks module does not depend on window
- SIP.js: pass window only to modules that depend on it

see https://github.com/joseph-onsip/SIP.js/commit/b6bb050745f07437703829675627d36fa20f236c