Explore using webworkers for PouchDB

[flimzy]

PouchDB supports webworkers. Some investigation should be done as to whether using one or more webworkers (in a pool?) would improve document read/write performance.

[flimzy]

It seems the worker-pouch adaptor won't really work for this project, as it does not work with other plugins (and this project uses the find plugin).

I think this means the only way to accomplish this for our project is to create my own abstraction layer which proxies requests to a web worker. The good news is, this should also make it possible to manage a pool of workers.

[flimzy]

As of #59, I'm no longer using the find plugin, so the worker-pouch plugin may again be an option (until 'query' is put in its own plugin)