refactor(client): Move all mixins to `views/mixins` from `lib`

* They just make more sense here.

fixes #1287
fix(client): Remove the ability for IE8 and IE10+ to show the password field.

Add the `no-toggle-pw` class to the body if the browser does not support toggling the password field type.
Add the `reveal-pw` which indicates the browser has its own password show mechanism. Hard coded to >= IE10.

fixes #1114
fixes #1015

.
Merge pull request #1288 from mozilla/issue-1287-move-view-mixins

refactor(client): Move all mixins to `views/mixins` from `lib`
Merge branch 'master' into issue-1114-ie8-password-toggle
Merge branch 'issue-1114-ie8-password-toggle'
fix(client): Check the user's old password before attempting a change password.

* Add 'checkPassword' to fxa-client.js
* Check the user's pasword before checking whether the passwords are the same.

fixes #1118
Change `assert.ok(false,` to `assert.fail`. Thanks @zaach!