Change Detection: perf, fix, style

Edit: The 2 lasts commits are about improving perfs:
1. by using regular fns over getters/setters. The speed gain is impressive in FF, Chrome is a little bit slower but still much faster than FF,
2. by inlining `isPresent()` and `isBlank()` where there is no need to test for `undefined`

Note: benchpress results sometimes vary from a run to the next, especially with FF. 
You have to notify the dispatcher before getting the next record. The reason is that the dispatcher can change the next record by, for example, enabling it. 

Consider this

```
a  <- group 1
b  <- group 1

c disabled   <- group 2
d   <- group 2
```

Let's say when we notify the dispatcher about `group 1` it enables `c`.

The more realistic example is probably adding or removing ranges.