Removed configuration for SPDY/2.
Introduced configuration properties for ALPN/NPN advertised protocols.

No more need to copy protonego-alpn.xml to a jetty.base to specify
which protocols are advertised.
Instead, simply specify:

protonego.protocols=h2-14,http/1.1
protonego.defaultProtocol=http/1.1

in start.ini (in the example above for http2).