Feature/4923 spv post deletion

Fixes issue 4923 by adding a 'delete post' button to the SPV if the author is logged in, and both a 'hide post' and 'ignore user' button if the user is not the author. 'Hide post', 'remove post', and 'ignore user' redirect the user to their stream.

'Ignore user' uses a different icon than the one shown on posts in the stream. I couldn't find the icon of an appropriate size, so I used entypo's mute icon.

Added some tests in spec/javascripts/app/views/single_post_actions_view_spec.js for testing the UI elements.

![del-post](https://cloud.githubusercontent.com/assets/1899810/3211319/115176ec-ef10-11e3-929c-94e5c28778b8.png)
![hide-post](https://cloud.githubusercontent.com/assets/1899810/3211320/1152cac4-ef10-11e3-8d9c-8bb29852672d.png)

I wonder if the ajax call shouldn't be moved into the model and replaced here too: https://github.com/diaspora/diaspora/blob/63c44d9f6bc2d7c218cac32104f544c8063e4f75/app/assets/javascripts/app/views/stream_post_views.js#L100