remove unmaintained reader app

This app hasn’t seen any updates in the last months. Also @priyanka-m doesn’t seem to react to pull requests (#1070) and @j-ed doesn’t seem interested in maintaining it.

Apart from that, there seems to be an existing reader app which is up to date in the app store: http://apps.owncloud.com/content/show.php/EPub+and+Comics+online+reader+%28oc5%29?content=157609

Hence we should remove this outdated code here.