Bug 1084298 - [Messages] Decoupling the all inputs query logic from DOM tree structure

- Add map for each view for maintaining the data for rendering/selection
nit: it looks like it can be quite heavy operation if we have a lot of checkoxes (iterate through all ids, stringify every id, create new ```Set```), maybe having method instead of property would be less misleading for developer? I usually expect property invocation to be blazing fast and to not depend on data size.

Thinking more about this method, it can be inefficient if you have 100 checkboxes with only one selected, in this case you'll have to iterate through all 100 :) Maybe we can improve it a bit, like below or smth better:
```
var allItemCount = 0;
var selectedCount = this.selectedCount;
for(var id of this.getInputIdIerator()) {
  if (++allItemCount > selectedCount) {
    return false;
  }
}
return true;
```

What do you think?