Refactor modify aspect facebox

Now that contacts are not visible to each other by default (see https://github.com/diaspora/diaspora/issues/4343), the user has to be able to change visibility easily. This can be done in the "edit aspect facebox", available in my_aspects view when hovering an aspect. I added it to the contact page too with https://github.com/diaspora/diaspora/issues/4397, but I still thought that the padlock to change visibility was not enough clear.

This PR goes from ![d-screen](https://f.cloud.github.com/assets/930064/1458095/e37a1ed0-4353-11e3-8aed-7bd9e0649a1c.jpg) to ![screen](https://f.cloud.github.com/assets/930064/1458096/e56e4dba-4353-11e3-8018-4f2c5b324eb8.jpg).

I also improved the text displayed when the user hover the button.

This PR also includes minor design arrangements and refactor of all the css from application.sass to facebox.scss, improving #3796