Improve CompanyUser display and add searching [MJ-819]

Searching works on user email and company name. This might be a little odd when first and last names are displayed.

I could add a link to the www.my.jobs admin for companies, but I'm pretty sure that is not desired.

![2014-04-02-095911_1150x275_scrot](https://cloud.githubusercontent.com/assets/3379265/2591804/18cd8a26-ba6f-11e3-941e-b3ba503a717a.png)

All tests pass.