Fix tag overflow

I think I've got a fix going for the tag overflow problem. I used browser width 1088px and 640px as breakpoints to show 10 and 5 tags respectively. Then I added a "show all" link. I also changed where the margin was placed to properly space the tags when it goes to multiple lines. Let me know if you have any comments!

10 tags:

![screenshot 2014-12-09 21 35 32](https://cloud.githubusercontent.com/assets/816517/5370185/e7801b20-7fec-11e4-9472-f45eb0d2c074.png)

10 tags expanded:

![screenshot 2014-12-09 21 35 36](https://cloud.githubusercontent.com/assets/816517/5370188/f42ffcaa-7fec-11e4-9eca-826a806bba58.png)

5 tags:

![screenshot 2014-12-09 21 35 55](https://cloud.githubusercontent.com/assets/816517/5370191/fe0d56e6-7fec-11e4-819d-459dee15d75c.png)

5 tags expanded:

![screenshot 2014-12-09 21 35 59](https://cloud.githubusercontent.com/assets/816517/5370198/0594d790-7fed-11e4-83d8-bd6a5b12de8f.png)


Could you localize this? Just add the key to `config/locales/en.yml` and use it here like: `<%= t("tags.show_more") %>`. I'll add the Dutch translation later