FEATURE: Mark All as Read button for Notifications page

Added a Mark All as Read button to the top/bottom of the notifications user page
https://meta.discourse.org/t/possibility-to-selectively-or-completely-mark-notifications-as-read/20227

Remove notifications property (no longer used)
Don't use __container__ instead use needs: ['user-notifications'], (thanks eviltrout!)
UX Improvement: Autofocus the topic field on edit

- After clicking on the pencil icon to edit a topic, the focus is not set on the input.
- This leads to cases where using keyboard shorcuts (e.g. cmd + left) leads to navigation instead.
- Searching around online, it seems the cleanest way to add a text-field that autofocuses is to create a component.
- I followed the [cookbook](http://emberjs.com/guides/cookbook/user_interface_and_interaction/focusing_a_textfield_after_its_been_inserted/) and did the most naive implementation.
- This focuses the text-field but at the start of the input. Setting selectionStart and selectionEnd solves this problem, but does not work on IE 8 and below.
Merge pull request #2878 from daemonsy/daemonsy_focus_topic_input

UX Improvement: Autofocus the topic field on edit
Merge pull request #2874 from cpradio/clear-notifications

FEATURE: Mark All as Read button for Notifications page