Feature type answer fixes, issue 1508, v2

This extends PR #304.
The extra changes:

* Use the `android:imeOptions="actionDone"` to hide the soft keyboard on enter/return presses. Also use that to show the answer. This is similar to the behavior of Anki desktop.
* Also, get rid of the visible `[[type:NN]]` by doing the comparison even when the type answer is switched off.

I may or may not write some code to bring the actual comparison in line with Anki desktop, but no guarantee. So maybe people want to wait a bit for that.

Extra notes:

* Unfortunately, i can't test this with old Android versions, as my Java seems to be broken
* You may want to look at the diffs wit [`?w=1`](https://github.com/ospalh/Anki-Android/compare/ankidroid:develop...feature-type-answer-fixes?w=1) to hide the whitespace changes.