provide method ContextManager#getCurrentViewFilter()

to provide correct viewing of reasons of JDTS filters in a special viewer we need to know the current view filter chosen in the "View Filter:" combobox (All Tests, Current Configuration, Current Template, etc.)
A special enum may be created to define the possible values of the method #getCurrentViewFilter(), e.g.
public static enum ViewFilter {
allTests,
currentConfiguration,
currentTemplate,
// ...
}