TASKMAN-17: Improve task view for Flamingo

This a part of https://github.com/xwiki-contrib/application-task/pull/5 by @maximaker about [TASKMAN-17](http://jira.xwiki.org/browse/TASKMAN-17).  Another pull request is coming for [TASKMAN-18](http://jira.xwiki.org/browse/TASKMAN-18).
OK, I'll modify https://github.com/xwiki-contrib/application-task/pull/12 and https://github.com/xwiki-contrib/application-task/pull/13.