Feature/top panel

- [ ] Ready to merge

TODO:

- [x] jsbin.settings.gui.toppanel to save the state open/close of the panel
- [x] save jsbin.settings.gui.toppanel in localStorage
- [x] css animation
- [x] responsive design of the content
- [x] Dave spinner not visible when panel is open
- [x] javascript to close/open panels and esc keybinding
- [x] Dave and file button as two distinct buttons
- [x] Test on old IEs (down to 8)
- [x] Border of the two buttons must be collapsed
- [x] Template for content
- [x] Make content dynamic (in order of required tasks)
  - [x] Structure of the object for the content (features, pro, blog, help, twitter, quote)
  - [x] Load content from JSON file (at this point - let @remy know as we may be able to avoid memcache)
- [x] Fix #1560
- [x] Columns of content are fixed (currently buttons under Dave move)
- [x] Links to open in same tab if same domain of jsbin, otherwise open in new tab
- [x] Pro features title will not include price in the json, but it'll be hardcoded in the html to not be visible to pro users

Not doing at the moment:
- [ ] Open bin dropdown
- [ ] List of last 10 bins
- [ ] fallback of jsbin.settings.gui.toppanel for old browser with no localStorage
- [ ] Read the content from memcache
- [ ] Test updating the content in memcache and content is correct in the header
- [ ] Make it work on IE7 ?


TEST CASES:

Loading of the html/js code
- At the moment:
   - Anonymous users don't have the panel
   - Normal users don't have the panel
   - Team users: have the panel
- In the future:
   - Both anonymous users and registered users will have the panel

Showing/hiding the panel
- Cookies/localStorage disabled: panel is closed
- First time user loads the page, with no settings in db/localStorage: panel is open
- Following time user loads the page:
   - if the last time he has closed the panel (both via esc or X button), panel is close
   - if the last time he has opened the panel, panel is open
- If for some reasons there are no settings about the panel, panel is open