implement maximumReconnectInterval and accelerationStrategy support on Configuration and Xhr

[hthetiot]

See #101 for details spec

Main logic entry point:

• https://github.com/kaazing/http2-cache.js/blob/features/fallbackOnConnectFailure/lib/xhr.js#L386
• https://github.com/kaazing/http2-cache.js/blob/features/fallbackOnConnectFailure/lib/configuration.js#L156

[hthetiot]

Need to check config.proxy exist before forEach

[hthetiot]

Via @dpwspoon

When in the accelerationStrategy: connected it looks like any initial requests that beat the establishing the initial ws connection/attempt will bypass the cache. (correct me if I’m mistaken).

This will add more load to the origin server then I was expecting as all browsers in that mode on initial startup might make requests directly to origin even though they will switch back to being accelerated shortly.

Perhaps we should wait for the first attempt to succeed or fail before falling back OR add a new acceleration strategy that does that

[dpwspoon]

Looks ok to me