Log scale tagging

This is the same commit as before except this time I tested it in the vagrant image and I think it looks considerably better than what is currently live. See for yourself.

![screenshot from 2014-12-13 03 27 09](https://cloud.githubusercontent.com/assets/79513/5423553/77880a6a-8278-11e4-8146-d6a167fd4f7c.png)

There is an actual distribution of sizes and not just one or two giant tags in the most popular tab.

One note: the instructions on the wiki don't mention a few things you have to do. I'll list them here in case someone else hits it later. You have to run "Tag.add_missing_filter_taggings" followed by "FilterTagging.update_filter_counts_since('1970-01-01')"  (obviously after running the datbase migrations) for the tag ui to work from a fresh vagrant image. Took me a while to figure that out.