Prevent duplication of cells while filtering

[Griff0ly0n]

Certain elements in an 'ember-collection' based list is rendered more than once, when filtering is performed on the list. I noticed this issue when i tried to use 'ember-collection' inside 'ember-power-select'. Below images depict this issue,

List showing duplicates

Duplicates in DOM

I traced down the root cause of this issue being related to presence of 'cellMap', which seems to be a lookup to check if the cell is already being rendered or not. Avoiding this lookup when inserting new items, resolve the issue.