fix(Scope): $broadcast and $emit should set event.currentScope to null

When a event is finished propagating through Scope hierarchy the event's `currentScope` property
should be reset to `null` to avoid accidental use of this property in asynchronous event handlers.

In the previous code, the event's property would contain a reference to the last Scope instance that
was visited during the traversal, which is unlikely what the code trying to grab scope reference expects.

BREAKING CHANGE: $broadcast and $emit will now reset the `currentScope` property of the event to
null once the event finished propagating. If any code depends on asynchronously accessing thei
`currentScope` property, it should be migrated to use `targetScope` instead. All of these cases
should be considered programming bugs.

Closes #7445
Closes #7523
docs(ngRoute): $routeParams is Object.<string, string>

Closes #7386
docs(guide/concepts-module-service.png): Typo in image

The ng-app was called ng=app in diagram image.

Closes #6473
Closes #7528
docs(tutorial/step-5): update image to match code

Closes #2753
docs($compile): remove reference to ngRepeat providing compile function

ngRepeat no longer has the compile function in its directive definition
object, since it retrieves its transclusion via the link function.

Closes 5638
docs(guide/expression): mention the ternary operator

Closes #6498
chore(rootScope): fix grammar in a test description

it's -> its

☆.。.：*・゜☆ Yeah, why not ☆.。.：*・゜☆

Closes #7534
docs(tutorial): add instructions for running node in Debian-based distributions

Specifying command for Debian based distributions, like Ubuntu, Mint, etc.

☆.。.：*・゜☆ Fantastique! ☆.。.：*・゜☆

Closes #7422
docs(tutorial): add <span> to index.html to match phonecat step4

Add missing <span> to app/index.html to match actual code on github

☆.。.：*・゜☆ Merci beaucoup! ☆.。.：*・゜☆

Closes #7520
docs(guide/$location): clarify "$watchers" / "$observers" terminology with links

Add links to API docs for Scope#$watch and Attributes#$observe in $location in order to clarify
the meaning of that terminology.

Closes #7497
docs(ngModelController): fix indentation code block

Closes #6660
docs(ngRepeat): fix formatting
docs(guide/services): fix link to minify Wikipedia page

Closes #7488
docs(guide/concepts): clarify definitions

Closes #7483
feat(ngMock): add support of mocha tdd interface

Closes #7489
docs(guide/concepts): clarify definitions
docs(guide/concepts): The service is `finance2.js`

Closes #7470
docs(): mention implicit usage of
docs(ngModelController): use `$sce` and `$sanitize` in the `contenteditable` example.

Closes #7464
docs(shallowCopy): fixed typo

Closes #7456