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
it's funny, but my IDE hightlights ```set``` as reserved keyword, but per JS spec it's not :)

Also we can probably simplify it a bit with ```for ... of...```,
```
var itemIdSet = new Set();
for(var id of this.getInputIdIerator()) {
  itemIdSet.add(id.toString());
}
return itemIdSet;
```

It's kind of sad that we have to stringify, otherwise it would be ```return new Set(this.getInputIdIerator())``` :)