SeaMonkey 2.15 Beta 1

# SeaMonkey-specific changes -
- SeaMonkey can be set as default client/browser on Mac and Linux now.
- See the changes page for minor changes.

# Mozilla platform changes -
- Preliminary support for WebRTC has been added.
- Image quality has been improved through a new HTML scaling algorithm.
- CSS3 Flexbox has been implemented.
- Support for new DOM property window.devicePixelRatio has been added.
- Support for @supports has been added.
- Startup time has been improved through smart handling of signed extension certificates.
- HTML5: Support for W3C touch events has been implemented, taking the place of MozTouch events
- Insecure content loading has been disabled on HTTPS pages (see bug 62178).
- Fixed several stability issues.