modify view `cp_files` in module cp_content #1495

#1495

I was unable to get the `Global: combine filters` filter to work to combine file and post search.

#### Changes:

* Removed 2 exposed sort options, in favor of sortable table headers.
* Added new exposed filter for "Used in" field (filter label "Used in").
* Added new exposed filter for media type (filter label "Type").
* Updated search textfield label to "File name or title" (was "File name or field")
* Updated link column to have heading "Link to share" (was blank)
* Enabled filter autosubmit for exposed filters.

#### Before

![screen shot 2013-10-17 at 3 16 01 pm](https://f.cloud.github.com/assets/228733/1355330/56d71a6e-3764-11e3-9206-a3df75595437.png)

#### After

![screen shot 2013-10-17 at 3 43 19 pm](https://f.cloud.github.com/assets/228733/1355333/6c98adb8-3764-11e3-9c3b-fb8699de1c1a.png)