Introduced "globalInitializerClasses" next to the existing "contextInitializerClasses", applying to FrameworkServlets as well

Issue: SPR-11314
Polishing
checkNotModified needs to consider HEAD as well

Issue: SPR-11317
Added tests for context initializers on DispatcherServlet

Issue: SPR-11314
Polishing
Several ref doc fixes

Issue: SPR-8182
Issue: SPR-11243
Issue: SPR-11292
Issue: SPR-11318
Fixed version number in xsd comment