Provide proper reuse of convertView - or remove convertView

[slodge]

Currently the convertView situation looks buggy to me:

1. It appears that the type of view being reused isn't checked before reuse (I might be wrong on this - I haven't yet fully understood the code!)
2. When views are reused it seems that member variable updates and event subscription/unsubscription isn't fully handled in all cases

I think these current problems aren't that important for small dialogs, or for dialogs used in one-pass update/refresh cycles.

However, for Mvvm - where individual fields will be updated - then this seems very important to me.