Do not use Assert.fail(), just leave it empty so we get a warning

(Reasoning: until all tests are done, it's easier to differentiate the
warning for no tests from errors on broken tests)
Change the way tests are imported
Unit tests for the cross-platform parts of HttpResponse and HttpRequest

The rest will be tested in a separate platform-test repo
Unit tests for HttpCookie
Small fix for multivaluemap
Changes to YesBoss, unit tests
Compile unit tests to client JS (and add conditional compilation as required).

Note: it looks like it will be worth implementing some alternative
`ufront.sys.File` and `ufront.sys.FileSystem` stuff that is ready
to work async in NodeJS (or even emulate a FS on a client?)