Data element and associated interfaces should be moved

Created by: jayjaybillings

The IDataElement and associated elements should be moved to an interfaces project, such as org.eclipse.ice.data, so that clients can use the interfaces without interacting with the dev.annotations project.

I'll assign this one to myself, but help would be appreciated so that I don't mess up any on-going work on the processors.

Note that there is some RDF-related code in the data project that I need to move. It is from my thesis work and I hope to rewrite it to use the annotation processors, so I'll figure out what to do with it.