Created a separate content manager for simple projects. Simple projects
are no longer handled with the same content manager as templates, and
are also installed in a separate directory in a workspace
.metadata/.sts. This solves various problems with simple project content
not available when starting the new spring project wizard. It also
solves the problem of having obsolete simple projects in the install
directory, as those are ignored if they do not match the descriptors
listed in the wizard plugin descriptor.xml for simple projects. Fixed
various other issues, and code clean up. Also changed the simple project
zips, so that they do not contain content, and only list the Spring
library dependencies.