Add read more link to index and cover image to posts

Hi,

I made some changes to theme to include the sidebar with cover image in posts. You can see it live at [jessek.co.nz](http://jessek.co.nz).

- Added Read more link to index
- Add sidebar to base.html with site name and social links
- Add sidebar block for additional sidebar content e.g. author name, date
- Update responsive css of sidebar to accomodate additional content

I'd be happy to discuss these changes and make improvements. I haven't checked what this theme looks like with gravatars enabled. I could also split the sidebar refactor and the read more links up in to separate requests.

## Main site
### Index
![index](https://cloud.githubusercontent.com/assets/2769942/2938045/51b41e36-d8ec-11e3-8cdb-b1dc79aabdb7.png)
### Post
![post-sidebar](https://cloud.githubusercontent.com/assets/2769942/2938048/51bd1554-d8ec-11e3-8e2f-3b8398e54ffd.png)

## Mobile view
### Index
![mobile-index](https://cloud.githubusercontent.com/assets/2769942/2938046/51b75aba-d8ec-11e3-9a44-2b9e28a430f1.png)
### Post
![mobile-post-sidebar](https://cloud.githubusercontent.com/assets/2769942/2938047/51bb46f2-d8ec-11e3-9360-04404aa203ca.png)