(#1614) shell: Log promises when resolved

Patches `toPromise` utility and the `PouchDB` constructor to log promise results.
Patching of the constructor was need to control which methods log (i.e. only a few of public methods) and also to pass info about where did that log come from.

Another approach that I tried was to have a custom eval in the repl. But from the [default implementation](https://github.com/joyent/node/blob/master/lib/repl.js#L114), the design does not look override/reuse friendly. I can't just intercept the