[js/Cu.evalInSandbox/v1.00] initial commit

branch `js/Cu.evalInSandbox/master` refactors components:
* Base_Sandbox
* HTTP_Request_Sandbox
* HTTP_Response_Sandbox

to evaluate user-defined javascript from within
an unprivileged Sandbox principal.

related APIs:
* Cu.Sandbox
* Cu.evalInSandbox

this is in contrast to the original code,
which uses `eval()` from within the addon's privileged scope.
This older version has been migrated to the branch `js/eval/master`.