fix($interpolate): don't ReferenceError when context is undefined

546cb42 introduced a regression, which would cause the function returned from
$interpolate to throw a ReferenceError if `context` is undefined. This change
prevents the error from being thrown.

Closes #7230
Closes #7237
fix(injector): invoke config blocks for module after all providers

This change ensures that a module's config blocks are always invoked after all of its providers are
registered.

BREAKING CHANGE:

Previously, config blocks would be able to control behaviour of provider registration, due to being
invoked prior to provider registration. Now, provider registration always occurs prior to configuration
for a given module, and therefore config blocks are not able to have any control over a providers
registration.

Example:

Previously, the following:

   angular.module('foo', [])
     .provider('$rootProvider', function() {
       this.$get = function() { ... }
     })
     .config(function($rootProvider) {
       $rootProvider.dependentMode = "B";
     })
     .provider('$dependentProvider', function($rootProvider) {
       if ($rootProvider.dependentMode === "A") {
         this.$get = function() {
           // Special mode!
         }
       } else {
         this.$get = function() {
           // something else
         }
       }
     });

would have "worked", meaning behaviour of the config block between the registration of "$rootProvider"
and "$dependentProvider" would have actually accomplished something and changed the behaviour of the
app. This is no longer possible within a single module.

Fixes #7139
Closes #7147
feat(NgMessages): introduce the NgMessages module and directives

The ngMessages module provides directives designed to better support
handling and reusing error messages within forms without the need to
rely on complex structural directives.

Please note that the API for ngMessages is experimental and may possibly change with
future releases.
docs(Attributes): ensure code sample is not escaped

Closes #6649
feat($interpolate): add optional allOrNothing param
fix(ngSrc, ngSrcset): only interpolate if all expressions are defined

BREAKING CHANGE

If `bar` is `undefined`, before `<img src="foo/{{bar}}.jpg">` yields
`<img src="foo/.jpg">`. With this change, the binding will not set `src`.

If you want the old behavior, you can do this: `<img src="foo/{{bar || ''}}.jpg">`.

The same applies for `srcset` as well.

Closes #6984
fix(ngSanitize): encode surrogate pair properly

The encodeEndities function encode non-alphanumeric characters to entities with charCodeAt.
charCodeAt does not return one value when their unicode codeponts is higher than 65,356.
It returns surrogate pair, and this is why the Emoji which has higher codepoints is garbled.
We need to handle them properly.

Closes #5088
Closes #6911
docs(ngModelOptions): correct typo

Closes #7335
fix(ngModelOptions): initialize ngModelOptions in prelink

Input controls require `ngModel` which in turn brings in the `ngModelOptions`
but since ngModel does this initialization in the post link function, the
order in which the directives are run is relevant.

Directives are sorted by priority and name but `ngModel`, `input` and `textarea`
have the same priority. It just happens that `textarea` is alphabetically
sorted and so linked before `ngModel` (unlike `input`).

This is a problem since inputs expect `ngModelController.$options`
to exist at post-link time and for `textarea` this has not happened.

This is solved easily by moving the initialization of `ngModel` to the
pre-link function.

Closes #7281
Closes #7292
test(ngModelOptions): fix e2e test focussing
fix(ngModelOptions): enable overriding the default with a debounce of zero

Because of how the logic was set up, a value of `0` was assumed to be the
same as `undefined`, which meant that you couldn't override the default
debounce delay with a value of zero.

For example, the following assigned a debounce delay of 500ms to the `blur`
event.

```
ngModelOptions="{ updateOn: 'default blur', debounce: {'default': 500, 'blur':
0} }"
```

Closes #7205
docs($interpolate): fix bug in example

Closes #7342
docs(directives): fix code lang matching

Closes #7339
docs(tutorial/step-07): fix typo in route pattern

One instance of `/phones/:phoneId` erroneously had a singular version,
`/phone/:phoneId`, which does not match what was actually used in the code.

Closes #7313
docs(tutorial): move bower_components into app folder