Make the PBKDF2 parallel test compatible with the web-workers implementation of paralleljs

This makes the PBKDF2 tests pass in the browser when compiled as a
browserify bundle.

 * Create a browserify module for the PBKDF2 lib which can
   be importer from a web worker context when running the test in the
   browser.

   Add this to the list of scripts to import into the worker.

 * Fix a typing error where the keyBlock() function returned an
   ArrayBuffer but the par.map() handler expected a Uint8Array.
   This happed to work with NodeJS because the ArrayBuffer
   was passed to the parent process via a JSON serialization and
   the result happened to be compatible with the Uint8Array interface.
Make the interface for deriving the encryption key for the master key async

In preparation for making this computation non-UI blocking
and faster by farming it out to web workers, make the interface
to it in onepass.ts async.