feat($compile): add notIsolated variant of directives

Added to the directive definition object the following attribute:
  - `notIsolated` - may be truthy or falsy, and therefore, defaults to falsy.

When declaring a directive definition object with a truthy `notIsolated`
property, whatever scope attributes the directive declares will be bound against
not an isolated child scope, but a normal child scope. This is a necessary
feature if Angular is to support directives that transclude into the trascluded
content of other transcluded directives, each of which may have bound directive
scope attributes.

For example, say you have a directive, called outerDirective that has scope
attributes. And say this directive's template uses another simple directive,
innerDirective that transcludes its content. And here's the kicker: say
outerDirective transcludes its content somewhere inside its innerDirective.

If this is the case, without declaring outerDirective with `notIsolated: true`,
its transcluded scope will be a child of outerDirective's isolate scope because
the outerDirective's transcluded content is transcluded into the transcluded
content of innerDirective. I admit it's a little circuitous to explain.

Therefore, Angular directives like outerDirective that have scope attributes and
transclude into the transcluded content of a nested transcluding directive need
to be able to be declared with `notIsolated: true`, otherwise the content
transcluded into the outerDirective won't be able to access the scope attributes
of the outerDirective's scope.

No breaking changes; although, considering the number of StackOverflow issues
that come from developers' inability to quickly grasp the concept of isolate
scope, `notIsolated` could be less awkwardly worded as `isolated` and then not
isolating any directive's bound scope would be an opt-in rather than opt-out
decision. But purely for the sake of not breaking any existing Angular code out
there, this non-isolating variant of directives is of course named to be
entirely opt-in.