Update CHANGELOG.md

Added missing changelog for the 0.6.1 release.
refactor(switch): refactor to match new spec
amend(attachDrag): add ios click fixes

Addresses #321
amend(switch): make click listening less sensitive (#321)
fix($$interimElement): make templates work with custom interpolation symbols

Previously, components specifying their own templates (such as Dialog, Toast etc) assumed that the
interpolation start-/endSymbols where `{{` and `}}`, thus breaking in apps using custom symbols.
This commit introduces a new `$mdUtil` method for replacing the "assumed" symbols (`{{`/`}}`) with
the actual ones.

Close #877.
docs(guides): several fixes (links, typos, syntax, line lengths)

Close #837.
fix(filenames): updated component .scss names to match conventions
Update README.md
fix(checkbox): added css support for disabled states

Close #888.
update(project): move 'themes' into 'src/themes'
enhance(bower): add project-level bower configuration

Close #902.
enhance(docs): add component template assets for fast-starts
enhance(docs): add version # and date of doc build

Close #940.
enhance(docs): improve use of promises in buildConfig.js
docs(dialog): fix toast references

closes #773
fix(switch): only add focus border if label is not empty

Closes #944.
fix(checkbox): only add focus border if label is not empty

Closes #944.
fix(layout): `flex="n"` attrs set height for column layout, width for row

Closes #937
docs(sidenav): updates $media to lock left sidenav on larger displays

Closes #948.
feat(theming): use $mdThemingProvider

BREAKING CHANGE: Themes are no longer defined by linked CSS files.

Themes are now defined through Javascript only. A 'theme template' is
bundled into angular-material.js, and then Javascript is used to
generate theme css for every theme the user defines.

The `default` theme is still shipped with angular-material.

If you used another theme (for example, the `purple` theme), change your code from this:

```html
<link rel="stylesheet" href="/themes/purple-theme.css">
<div md-theme="purple">
  <md-button class="md-primary">Purple</md-button>
</div>
```

To this:

```js
var app = angular.module('myApp', ['ngMaterial']);
app.config(function($mdThemingProvider) {
  //will use the colors from default theme for any color not defined.
  $mdThemingProvider.theme('purple')
    .primaryColor('purple');
});
```
```html
<div md-theme="purple">
  <md-button class="md-primary">Purple</md-button>
</div>
```

For more information, read the updated [theming
documentation](https://material.angularjs.org/#/Theming/01_introduction).