Web application support (targeted for FxOS)

- Landing page for the app
- The required app manifest
- SVG Logo provided by Scrollback
- Logos reworked for various resolutions
- Install script added to prompt installation
- MIME type fixed for serving manifest.webapp file
- Reduced & reused the default room join/create template

Signed-off-by: Soumya Deb <deb@applait.com>