Problems with first/lastVisible

[dhilt]

Both firstVisible and lastVisible adapter properties may produce sporadic errors resulting in "HTML element is not defined" message which makes the UI broken.

• in this case the error should not be critical (fixed by Adapter "wanted" container fixes. Part 2 #41)
• need to reconsider "wanted" contained on the Adapter, as it seems first/lastVisible are always requested by the Adapter in the end of the vscroll workflow cycle, even if there were no explicit calls for these props (fixed by Adapter "wanted" container fixes #40 and Adapter "wanted" container fixes. Part 2 #41)