Fixes bug 453524:
- created a preference page and a project properties page to manage problem markers in the Xtext grammar editor
- added a warning for bidirectional references
- moved issue identifier strings from XtextValidator to XtextConfigurableIssueCodes
- using addIssue(..) instead of error(..) / warning(..) in order to respect the user preferences
- added ConfigurableIssueCodesPreferenceStoreInitializer to DefaultUiModule
- fixed a problem in OptionsConfigurationBlock.hasProjectSpecificOptions(IProject)

Change-Id: I78c4681dfd2c0e9ad937662ed71d8c968463614b
Signed-off-by: Miro Spönemann <miro.spoenemann@itemis.de>
Merge "Fixes bug 453524: - created a preference page and a project properties page to manage problem markers in the Xtext grammar editor - added a warning for bidirectional references - moved issue identifier strings from XtextValidator to XtextConfigurableIssueCodes - using addIssue(..) instead of error(..) / warning(..) in order to respect the user preferences - added ConfigurableIssueCodesPreferenceStoreInitializer to DefaultUiModule - fixed a problem in OptionsConfigurationBlock.hasProjectSpecificOptions(IProject)"