docs about ion-toolbar always being first child on page

[jgw96]

We should add a note to the toolbar docs about the toolbar always needing to be the first child on a page. Related issue: ionic-team/ionic-framework#6392

[brandyscarney]

This is actually going to change with the next release since we're wrapping them in ion-header's. Also, the ion-content can be the first-child as well if there is no toolbar/header.

[brandyscarney]

We need to add documentation that a page should only have the following direct children:

<ion-header/>
<ion-content/>
<ion-footer/>

[mhartington]

This could be a good place for a general view component section in the component docs

Go over the anatomy of a view component and such.
Actually would this be a good fit for the component docs or the getting started guide?

[brandyscarney]

Related issues: #685 #676

[mhartington]

waiting on this before moving forward. #700

[mhartington]

Right now we have it noted in http://ionicframework.com/docs/v2/components/#toolbar