enable per-request tunnel url configuration

The configurable `tunnelUrl` value will still be validated against
`tunnelPrefix`, which can be configured in application.json and defaults to
`/tunnel`.
add history line items related to middleware changes for 0.5.7
Merge pull request #1047 from ekashida/tunnel-url-override-wip

enable per-request tunnel url configuration
upgrading to 3.9.1 to solve the issue with handlebars
Merge pull request #1048 from caridy/yui-390

upgrading to 3.9.1 to solve the issue with handlebars