Remove unused import and invalid Javadoc
Fix calls to 'toArray()' with zero-length array argument
Cleanup .css removing invalid selectors
Merge branch 'v2.1-dev' into v2.1-dev-2nd-attempt
Applied pull request from donald-w, thanks!
Patch by Edu Zamora: Fixes bug where the audio icons for sounds in the question disappear when showing the answer, making users unable to replay audios