See doc update in the diff for more info.

BREAKING CHANGE: jqLite#scope() does not return the isolate scope on the element
that triggered directive with isolate scope. Use jqLite#isolateScope() instead.

When an isolate scope directive is also a "replace" directive and at the root of its template
it has other directives, we need to keep track remember to use isolate scope when linking
these.

This commit fixes the leakage of this state when this directive is used again later inside
or outside of the isolate directive template.

Fixes an issue when we didn't share the isolate scope with the controller
of the directive from the isolate directive's template when this directive
was replaced onto the isolate directive element.

I had to fix one unit test, as it assumed the broken behavior, where application template gets the
isolate scope of other (isolate) directive, rather than the regular scope.

BREAKING CHANGE: Child elements that are defined either in the application template or in some other
directives template do not get the isolate scope. In theory, nobody should rely on this behavior, as
it is very rare - in most cases the isolate directive has a template.

Fixes issue with isolate scope leaking all over the place into other directives on the same element.

Isolate scope is now available only to the isolate directive that requested it and its template.

A non-isolate directive should not get the isolate scope of an isolate directive on the same element,
instead they will receive the original scope (which is the parent scope of the newly created isolate scope).

Paired with Tobias.

BREAKING CHANGE: Directives without isolate scope do not get the isolate scope from an isolate directive on the same element. If your code depends on this behavior (non-isolate directive needs to access state from within the isolate scope), change the isolate directive to use scope locals to pass these explicitly.

// before
<input ng-model="$parent.value" ng-isolate>

.directive('ngIsolate', function() {
  return {
    scope: {},
    template: '{{value}}'
  };
});

// after
<input ng-model="value" ng-isolate>

.directive('ngIsolate', function() {
  return {
    scope: {value: '=ngModel'},
    template: '{{value}}
  };
});

Closes #1924
Closes #2500

This refactors the filter guide docs into a single file.
Also removes out of date references to the fact that Angular used to enhance Arrays while evaluating expressions.

Before, there we multiple overview docs:
- guide/overview
- guide/introduction
- guide/dev_guide.mvc
- guide/dev_guide.mvc.understanding_model
- guide/dev_guide.mvc.understanding_view
- guide/concepts

Now we have:
- guide/introduction: High level description of Angular with the key benefits but without code or any concrete concepts
- guide/concepts: explains all important concepts with a simple example and contains deep links to the other parts of the guide.

 All the old information was moved into existing documents or deleted when they were duplicates.