Let’s style this thing!

The app could look, erhm, prettier. So let’s make it prettier! One could see this issue as a part of #35.

End result should look something like:
<a href="https://raw.github.com/opfo/resources/master/Mockups/Exports/Questions-list-view-20130507T0158.png"><img alt="The questions list" width="320px" src="https://raw.github.com/opfo/resources/master/Mockups/Exports/Questions-list-view-20130507T0158.png"></a> <a href="https://raw.github.com/opfo/resources/master/Mockups/Exports/Question-view-normal-20130507T0200.png"><img alt="The question view for a “normal” question" width="320px" src="https://raw.github.com/opfo/resources/master/Mockups/Exports/Question-view-20130507T0200.png"></a>

## Tasks
### General
- [x] Create a sprite sheet for all the image assets.
- [x] Export all the image assets.
- [ ] Change the font to Avenir Next, see pull request #29 and the tasks for each section. **In progress**

### Questions
- [ ] Rework the single question table view cell. **In progress**
  - See if we can get tags in there.
  - See if we can get last modified date in there.
- [x] Remove “Heat” button as that is now inline.
- [ ] Improve the “cool” color scheme.
- [ ] Improve the “bad” color scheme.
- [x] Change the font to Avenir Next, see pull request #29. **In progress**

### Question
- [x] Change the question header view to use our background image.
- [x] Style the vote up/down buttons.
- [ ] Set the <span style="color:#0069bf;">link color to `#0069bf`</span> (`0x0069bf`; HSB: 207,100,75).
- [x] Set the color of comments, poster and score to link color to `#404040 ` (`0x 404040 `; HSB: 0,0,25).
- [ ] Try to get last modified date into the design.
- [x] Change the font to Avenir Next, see pull request #29.

### Tags browser
- [ ] Change the font to Avenir Next, see pull request #29.

### Activity
- [ ] Change the font to Avenir Next, see pull request #29.

### Users profile search
- [ ] Change the font to Avenir Next, see pull request #29.

### User profile
- [ ] Change the font to Avenir Next, see pull request #29.
- [x] Change the font of the login view to Avenir Next, see pull request #29.
- [ ] Change the font of the sign up view to Avenir Next, see pull request #29.

### Tab bar
- [ ] Change the font to Avenir Next, see pull request #29. **Postponed as there is an issue in AKTabBarController, the version which allows us to set the font also has a bug which (is supposed to have been fixed, but it isn’t) pushed the contained view controller’s view down by the height of the status bar.**