Fix bugs

* fixed positioning bug in topic card
* fixed hover on delete-button
* added confirmation before deleting topic
* fix floating bug in navigation on mobile

@JonathanTR: 
Here, absolute positioning is the correct choice so the delete button will not increase the height of a card. The delete button should only be dependent on the card and not change the height of the card (which has overflow: auto; to adapt its height to its child elements 'size'). The button is a child of card so position: absolute; takes it out of the regular element flow and basically places it on top of the card (so it is e.g. always clickable and :hover works and such).

Also, in terms of good UX; such a destructive action should be placed in either the top-right or the top-left corner so the chance of users clicking on it by accident is minimized.  Our content is text-align: left; so the delete button should be in the top-right corner of the card. On that note, I added a confirmation to delete.

Sounds good?





![200](https://f.cloud.github.com/assets/3147345/1641770/6b04fae6-5862-11e3-9785-56c141b4c783.gif)