Revert "Fix item polishing"

This caused items like positioners and itemviews to not
relayout or update as appropriate when items were hidden,
and therefore caused problems all over in eg. controls.

This reverts commits
- 43f983350a548b1b663ea07a0e87e4cc58834214
- 01e609e9fa0ca1317e0f4eff4802a79584450357
- 439f31f128e70ecae16544ee7041695c60e0b2d6

Task-number: QTBUG-36954
Task-number: QTBUG-36934
Task-number: QTBUG-31830
Change-Id: If04cdce51206568c360a45e24efc0bd04764750b
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>
Canvas: do not emit paint signal when invisible

Task-number: QTBUG-31830
Change-Id: I23c6fc822547120f14c2d9a09f01a8f985745e2a
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>