ui.js in test kit

I’d like to include `ui.js` in the test kit so that we can exercise UI helper functions automatically. Up until now I’ve been placing some of these helpers on `miniLock.util` because `miniLock.UI` wasn’t available under test.

These changes let us add `ui.js` to the test kit. I’ve also moved the following functions from `miniLock.util` to `miniLock.UI` which is where I they I think they belong:

- `miniLock.UI.getBasenameAndExtensions`
- `miniLock.UI.summarizeRecipients`

And, a new test that demonstrates `miniLock.UI.readableFileSize` is also included.

Thoughts? Suggestions?