Initial commit of 'Selectable' filtering implementation

Initial commit of per-request / query parameter driven filtering implementation ("selectable"). As discussed, included in security filtering project.

May need a little cleanup around dealing with nested paths, but tests are passing.

You can start either the security or selectable implementation as follows:
```
mvn exec:java -Dexec.mainClass="org.glassfish.jersey.examples.entityfiltering.security.App"
mvn exec:java -Dexec.mainClass="org.glassfish.jersey.examples.entityfiltering.selectable.App"
```