Nextgen comment pick button

## Pick Buttons

This pull request adds comment pick functionality and UI to the nextgen discussion app.

### The functionality works as follows;

#### Assuming that:

1) [You are signed In](https://github.com/guardian/frontend/compare/nextgen-pick-button#diff-33d9c87117dd5f3ca53eb93b7cf7a1deR144)
2) [You are a 'Staff' user](https://github.com/guardian/frontend/compare/nextgen-pick-button#diff-33d9c87117dd5f3ca53eb93b7cf7a1deR99)

##### You will see Pick and Unpick options on comments in the all comments section.

---

#### Assuming that:

1) [You are signed In](https://github.com/guardian/frontend/compare/nextgen-pick-button#diff-33d9c87117dd5f3ca53eb93b7cf7a1deR144)
2) [You are a 'Staff' user](https://github.com/guardian/frontend/compare/nextgen-pick-button#diff-33d9c87117dd5f3ca53eb93b7cf7a1deR99)
3) You are looking at an unpicked comment
4) [You are *not* the comment author](https://github.com/guardian/frontend/compare/nextgen-pick-button#diff-33d9c87117dd5f3ca53eb93b7cf7a1deR163)

##### You can now Pick and subsequently unpick that comment.

![screen shot 2013-11-27 at 15 00 20](https://f.cloud.github.com/assets/1170410/1632229/bde69b82-5774-11e3-9bc6-7ce5ac031609.png)

---

#### Assuming that:

1) [You are signed In](https://github.com/guardian/frontend/compare/nextgen-pick-button#diff-33d9c87117dd5f3ca53eb93b7cf7a1deR144)
2) [You are a 'Staff' user](https://github.com/guardian/frontend/compare/nextgen-pick-button#diff-33d9c87117dd5f3ca53eb93b7cf7a1deR99)
3) You are looking at a picked comment
4) You are the user that picked the comment (API)

##### You can now unpick that comment

![screen shot 2013-11-27 at 15 00 35](https://f.cloud.github.com/assets/1170410/1632230/c5408514-5774-11e3-8e63-855514ba360d.png)

---

#### You may not:

 - Unpick a comment that someone else picked (API)
 - [Pick or Unpick you own comments](https://github.com/guardian/frontend/compare/nextgen-pick-button#diff-33d9c87117dd5f3ca53eb93b7cf7a1deR163)


![code-11](https://f.cloud.github.com/assets/1170410/1632299/a9a0a2a2-5775-11e3-9674-eda2df5f4671.gif)