EC2 Instance View - Configurable Columns

Adds a Configure Columns menu and action to the EC2 Instance View.
![screen shot 2014-03-13 at 10 44 08 am](https://f.cloud.github.com/assets/874068/2410567/833b05a2-aabe-11e3-82a5-2f5c2d5c8e73.png)

Allows user to select columns to be display (as well as specify tags to display as columns).
![screen shot 2014-03-13 at 10 45 03 am](https://f.cloud.github.com/assets/874068/2410579/a3ea88cc-aabe-11e3-97fb-00ebe5d50ac5.png)

Updates the Instance View according to the column configuration specified in the new menu.
![screen shot 2014-03-13 at 10 45 33 am](https://f.cloud.github.com/assets/874068/2410588/b83308c2-aabe-11e3-97f8-a44b30d4ca64.png)