fix: mouse navigation should be done on release

I'm actually not sure if it's a bug but anyway here is the patch.

Currently, Dolphin will navigate forward/backward if the user presses the forward/backward button on their mouse. Normally application will do mouse action only when the mouse button is released, e.g. when clicking a button, the button action will be triggered after the mouse button is released, not pressed. This patch will make Dolphin do navigation on mouse release.

I did a search on KDE HIG documentation but didn't find anywhere that described the intended behavior related to this issue (not sure if I missed something). Windows explorer.exe, Chrome/Chromium, Windows (legacy) Photo Viewer both did forward/back navigation on mouse release, but Firefox, QtCreator, IDEA-based IDE will do it on mouse pressed.

Please feel free to close this issue if action-on-pressed is by design :)