Add SaveDocument test to benchmark
Allow the RemoveCurrentSelection benchmark step to be disabled

This action is still extremely slow on large documents (100+ pages).
Remove unneeded loadClass calls
Rewrite RuntimTest.testWrite to not depend on the ByteArrayWriter class
Replace existing zip implementation with jszip v2.4.0

jszip has a much cleaner API than the existing RawDeflate version. In
addition, jszip supports creation of a compressed output stream.

As it's non-trivial to make jszip behave with closure compiler, a second
concat-only step has been during compilation to include any 3rd party
dependencies.

Fixes #21.