Allow multiple help filters to be selected

Currently, you can only apply a single filter to the help system, or view the content unfiltered. Each filter can only be configured combining multiple attributes using logical operator "AND".

When you have many Qt versions installed, but only use one or a couple of them very often, the help system either becomes hard to search (working unfiltered, providing lots of quasi-duplicate results from different versions), or you continuously have to switch filters (which is very tedious because of the location of the filter drop down, far from the place where you enter the search terms).

Consider that you mostly need the help system to look up content for "Qt 5.10 (all modules)", "Qt Creator" and "Qbs": How would you do that?

Since I see that creating a more complex filter that allows both "And" and "Or" operation between attributes isn't easy, I suggest to provide a way to select multiple active filters (which are combined using OR).