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
If we use the approach above then we can use ```this.selected = new Set(allKeys);``` since ```key``` and ```selectedKey``` should have the same type: either _string_ or _number_. Number sounds better for our particular use case, but string is more generic - so it's up to you :)