Clean up the clean up of the typed answer. Like this typing “<” &c. when...

Re-commit of one of the fixes from PR #396.

Should fix this  [complaint](https://groups.google.com/d/msg/anki-android/Gj-FYvj0NDQ/gInNwY8dWEAJ) about HTML-like answers for the type answer feature. This cleans up the clean up of the answer. The stored answer already has `&lt;`s &c. for `<`s. Do the same kind of replacement for the typed text.

This one does not remove the trailing whitespace from a line that was removed by another commit…