Dolphin Places: Make it easier to drag and drop items

When doing a drop, a check is performed to see if it is within x pixels
from the top or x pixel from the bottom of the rect. If it is, then the
drop is considered a drop between items.

This x was fixed to qMax( 4, myStyleOption.padding ) which would
generally be 4. This is fine for some cases, but when the rectangle size
increases then this 4 pixels is not enough. Hence this 'x' is now being
set to 30% of the rectangle height.

By default the rectangle height is 20 pixels, so x is now 6 instead of 4
in the default case, which does make it slightly easier.

Also, this in-between-items check is only performed when moving from one
item to another. This is not good since if you enter the item and the
bottom, the indicator is shown, and then as to start moving it up it
stops showing, and then it should start showing again as you approach
the top edge.

Modified the code to run the check on every mouse drag event even if the
hovered item has not changed.

Both these changes combined make it much easier to drag and drop items.

REVIEW: 110342