[jsieve] Merge into a single module

To simplify the use of this library for its consumers, it would be preferable to have only a single deployed jar.

Also, ideally there should be *no* external transient dependencies.

Steps to take:

1. Move what is relevant in utils to core
2. Rename “jsieve-core” to just “jsieve”
3. Rename “jsieve-util” to “jsieve-examples”

The examples module could still exist for those who may be interested, but should no longer be deployed as part of the library.