Making wtf.db.load async and fixing the async load flow.
This makes node.js apps work again, though with some modifications to
their load flow. Also adding a mock Blob object for node to get things
working there.

This removes the wtf-json and wtf-calls support, for now.
Merge pull request #337 from google/async_load

Making wtf.db.load async and fixing the async load flow.