Rationalize the java version used in the bnd nature repo projects

.classpath files are cleared of JRE_CONTAINER references. ee.j2se;
version=${javac.ee} used consistently.

Signed-off-by: BJ Hargrave <bj@bjhargrave.com>
Merge pull request #615 from bjhargrave/java-version-rationalization

Rationalize the java version used in the bnd nature repo projects