Fix use of 100-Continue in servers

The Expect: 100-continue request is sent by clients (mostly curl) when a large size body upload is expected.

We have it enabled in curl in our put requests by default (we should modify it only for uploads we know are explicitly large).

The server should only respond to this once - after receiving and parsing the headers. It looks like we're sending it as a way to say 'send more' generally - which causes multiple issues.

Fix it by allowing web views to independently respond to 'header' and 'body chunk' http events. Then we can issue redirects quickly to clients supporting Expect.