JBIDE-14990 : check existing source validity

Signed-off-by: Fred Bricon <fbricon@gmail.com>
JBIDE-14996 : Enable open cheat sheet on project import

Signed-off-by: Fred Bricon <fbricon@gmail.com>
JBIDE-15006 : use central wizards in offline mode

Signed-off-by: Fred Bricon <fbricon@gmail.com>
Bump parent pom version to Beta3

Signed-off-by: Fred Bricon <fbricon@gmail.com>