Android web app installation

[brehaut]

Users may wish to install the site into their mobile device of choice as an 'app'. To support this we need all assets for all android device sizes and metadata configured correctly.

Consult googles latest documentation for details

• [ ] Icons
• [ ] Startup Images
• [ ] installation metadata and manifest

Work with design team to determine whether we want full screen or browser chrome for installed apps. Do what seems appropriate for iOS separately from Android.

Icons and startup images should be based on site style and Alex Moon's hexagon/magnifying glass icon designs. See documentation wiki for visual style guide.

Depends on #11