EditFilterDialog improvements

[Daniel Faust]

Hi,

some time ago I filed a bug report regarding the behaviour of the ratings 
filter in the collection browser: https://bugs.kde.org/show_bug.cgi?id=238736
And I saw you already discussed that under the topic "How to get rating 
(stars) input from users?"

Now I also added KRatingWidgets to the EditFilterDialog and checked for 
further inconsistencies but found none (nighter in the Dynamic Playlist nor in 
the APG, they already handle it correctly).

I also added suffixes to the spin boxes, this should be most useful when 
filtering by file size or length (letting the user know the unit Amarok is 
using).

Furthermore I had a look at the "Between" mode (filtering between two values). 
Using it together with the invert check box caused the query to return an 
empty result. I added an "OR" and made the min and max values keep their 
values (don't increase/decrease because of the greater/lower sign).
But maybe disabling the invert check box in "Between" mode would be ok too.

The last problem I found is the handling of dates. Dates are converted to a 
days difference thereby increasing when going backwards in time. I find that 
unintuitive, the words "less than" and "greater than" don't suite neither.
The APG editor implements that nicely. The Dynamic Playlist uses the same 
words as the EditFilterDialog only that it handles the "less than" and 
"greater than" in the opposite way.

So please tell me what you think of my changes on the one hand and what you 
think is the best behavoir for the dates filter on the other hand.

Personally I would like to make it as it is in the APG everywhere.

Greetings
Daniel Faust