fix #728 Headers should not be shared between request handler instances

JSONRequestHandler used to have a headers which were implicitly static,
causing issues when modifying those headers with
RequestHandler#getHeaders().
fix #727 Callback failure when submitting a JSON request should be handled in the framework.

Close #731
refactor Rename some tests

Also fix a minor issue with MaximizableDialogTest which had template test
env set incorrectly.

Close #684.
fix #722 PageEngine animation CSS rules are added multiple times in the DOM
refactor TemplateInheritanceTest

Close #719.
feat #682 add `macro` to @aria:Dialog as an alias to `contentMacro`

To make API more consistent, let `macro` in @aria:Dialog be a synonym for
`contentMacro`. `contentMacro` still takes precedence.

Close #682. Close #687.