Auto added tiles should add at the end

Custom tiles that were added to QSTileHost were always added at the
beginning. Add a parameter so they can either be added at the beginning
(from StatusBar) or at the end (from AutoTileManager).

Test: manual
Test: atest AutoTileManagerTest QSTileHostTest
Fixes: 157497851
Change-Id: Ifb24d6dcca164d30f5888581654fe3e9c7489d4e