Adapt rwt.osgi and testfixture bundles to javax.servlet 3.1

javax.servlet 3.1 introduces some new abstract methods, which lead to
compile errors in the corresponding subclasses in rwt.osgi
(ServletContextWrapper) and testfixture (TestRequest, TestResponse,
TestServletOutputStream...)

- adjust javax.servlet version range
- add empty implementation for the new methods in ServletContextWrapper
and fixture classes

Change-Id: Ib560ccd245920c9aab32de528a252c0a7b7673a8
Signed-off-by: Ivan Furnadjiev <ivan@eclipsesource.com>
Change execution environment of JS test runner to Java 1.7

javax.servlet 3.1 requires Java 1.7.

Change-Id: I5448da9b3fa9f134bfcf0809779ce9a255d1ddd6
Signed-off-by: Ivan Furnadjiev <ivan@eclipsesource.com>