Update pre-ASF copyright notices
Make constants final classes instead of interfaces

This commit prohibits implementation of the empty interface and
instantiation of the class.  Refer to _Effective Java_ item 19 for
more background.
Migrate InputSupplier callers to ByteSource

A future version of Guava will remove InputSupplier.
Prefer Guava Files over FileInputStream

This ensures proper resource handling.
Don't fail on tag filtering when group is not specified.