Advanced search rebased

Adds the required search providers and search results for the new functionality in the Advanced Search app. To test, checkout the advanced_search_rebased branch on the 3rdparty, core, and app repositories. I have submitted parallel pull requests in [3rdparty pull #7](https://github.com/owncloud/3rdparty/pull/7) and [apps pull #520](https://github.com/owncloud/apps/pull/520).

This work overlaps some of the work @butonic did with the Lucene database but also adds the ability to search all types of search results in one pane. @jancborchardt see as well as these changes could eventually replace the AJAX search dropdown; for this to happen, I think the app would have to be included in core, since it would be a required app.