Add jellybeans color theme.

@edkolev - Thanks for this project. I'm pretty happy with how my tmux statusline looks right now!

Anyway, I added a color scheme to use with the [lightline.vim](https://github.com/itchyny/lightline.vim) version of the jellybeans vim statusline. I thought it might be useful to someone else, hence the pull.

Here's what it looks like:
![screen shot 2014-01-19 at 7 33 53 pm](https://f.cloud.github.com/assets/885841/1951567/b0c37ab2-8184-11e3-829a-7f6545aa062c.png)

I didn't look to hard, but I couldn't find an easy way to add a new colors scheme without modifying the plugin code. It might make sense to be able to specify a custom theme hash with a `let g:tmuxline_custom_theme = { ... }`.