Stops temporary containers being created needlessly due to API misuse.
For example, it’s common for developers to assume QHash::values() and
QHash::keys() are free and abuse them, failing to realize their
implementation internally actually iterates the whole container, allocates
memory, and fills a new QList.
Added a removeIf generic algorithm, similar to std ones. We can't use std
algorithms with Qt dictionaries because Qt iterators have different
behavior from the std ones.
Found using clazy.
Legacy SearchEngine class really has three roles:
1. Manage search plugins,
2. Handle the search job, and
3. Handle the download of the torrent file using the search plugin.
Now it is splitted into 3 classes: SearchManager, SearchHandler and
SearchDownloadHandler.
Search GUI is also improved.
