Only follow mouse when moved (Fixes Bug #372635)

Summary:
Use a new variable moved to detect if mouse moved and only change index if the mouse moved. This helps preventing index changes when only using keyboard to search something in milou and to not accidently start/open something you did not want (see bug report https://bugs.kde.org/show_bug.cgi?id=372635 )

BUG: 372635

In general the onEntered signal seems to be broken in Qt somehow as I could not make it work reliably with Qt 5.7.1. Sometimes it worked but mostly the code using onEntered failed to work with onPositionChanged (I guess this also does not always set it to true).
Hence I tried containsMouse which seems to work reliably at least on Qt 5.7.1.
Tests are appreciated especially on other Qt versions.

Reviewers: broulik, davidedmundson

Reviewed By: davidedmundson

Subscribers: ltoscano, qi437103, lfurmetz, anthonyfieroni, davidedmundson, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D5490