Introduce ConnectionConfiguration.

Expand the scope of TlsConfiguration to all connections, http: and https:.

Closes https://github.com/square/okhttp/issues/815
Closes https://github.com/square/okhttp/issues/1058
Merge pull request #1089 from square/jwilson_1013_connection_configuration

Introduce ConnectionConfiguration.
Only read hpack tests for the current draft.
Merge pull request #1093 from square/adrian.hpack

Only read hpack tests for the current draft.
Change Headers.Builder to be final.
Merge pull request #1095 from square/jw/final-headers-builder

Change Headers.Builder to be final.