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The device will respond to a non-WS request with a simple page that loads
websocket_content.js from a static host (http or https). However, even
if the resources are https, the page is still http and therefore allows
requesting to a WS (not WSS) websocket on the device.

Removed unused client_handshake from websocket_helper, and then merges the
remainder of this file (server_handshake) into webrepl.py (to reduce
firmware size). Also added the respond-as-HTTP handling to
server_handshake.

The default HTTP response is a simple page that sets the base URL and then
loads webrepl_content.js which document.write's the actual HTML.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>