🚧 [Do not merge] Add support for HTTP2

[abovedave]

This should give a huge performance boost to DADI Web! Would be nice to profile some builds before and after.

Closes #155.
Closes #174.
Closes #175.
Closes #158.
Closes #168.
Closes #173.

Features

• Support for HTTP/2 #155 HTTP2 support over SSL when config.server.http2 is true (and config.server.protocol is https) ¹
• Support for HTTP/2 #155 Introduction of config.globalPushManifest and page.pushManifest for pushing assets over HTTP2
• Rolled our own internal middleware (see /lib/view/public.js ³) for serving from the public folder - removed need for Express modules serve-static and serve-favicon.
• Changed & deprecated config.headers.useGzipCompression to config.headers.useCompression
• Added an internal helper called help.canCompress which determines if caching is enabled on the system and tests if the client can accept a compressed output
• Implement more efficient compression engine (brotli, by way of iltorb, fallbacks to Node's zlib for gzip if not available)
• For clarify, moved the helpers previously name sendBackJSON, sendBackHTML into view/send.js
• Removed the unused helper sendBackJSONP
• Added new compression engine to the response, removing need for Express's Compress middleware
• Static assets obey compression settings via config.headers.useCompression²
• Compressed responses are now cached, rather than being cached on each request
• Assets that have been compressed are cached, rather than being compressed on each request
• Public folder assets are only compressed if it will save space (checked using compressible)
• Removed outdated media path.
• Includes changes made by Process routes after middleware #168

To-do

• Fix tests
• Optimise & merge help/pushAssets and middleware/ServePublic functions
• Write test for HTTP2 push (example here)
• Add brotli compression to the main response
• Cache the compressed response Gzip/Brotli response before caching #158
• Implement pending fix for Assertation error from spdy

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1. Node supports H2 natively (scheduled for Node 8, discussion here)
   2. I think we should roadmap changing this to useCompression as we’re detecting and using Brotli where available Done

[abovedave]

Closed until Node supports http2 natively.