(Failing) tests for reflow.
Upgrade the version of mocha used in the tests.

This means that all the tests will run and means you don't get an error
along the lines of "1 of NaN tests failed".
Remove broken <script>s from the test runner.
Implement a simple line-based reflow algorithm.

The reflow algorithm looks at each line and the next to determine
whether the newline is soft or hard; it's simple, but it should work in
90-95% of all cases.
Hook text reflow into the message view.

This should make the mobile reading experience much more pleasant since
there won't be line breaks in the middle of things. Fixes #83.