Improve support for "Other downloads"
* Replace DownloadUtils.getDownloadStatusNoRate with DownloadUtils.getDownloadStatus to show download rate anywhere (and don't modify DownloadsViewItem.prototype._updateStatusLine() anymore)
* Override DownloadsSummaryData.prototype._updateView() to mark paused "other downloads"
(WIP for #1)
Rename preference: "detailedText" -> "showDownloadRate"
(related to #1)