Add wrapper class input to media filter

I started to look into coding this but didn't have the chops. So, here's my proposal:

In #1421786: display fields when embedding with WYSIWYG embedding full view modes (with their fields) was included, but we ended up with a problem where most images inserted via the WYSIWYG are floated (or otherwise positioned). This causes problems, however, when you include fields because floating the image does not float the fields (the entire view mode embed needs to be floated or otherwise positioned together).

Rather than hardcoding float presets, I propose a more flexible solution. It includes:

1. add a textfield to the media browser embedding form where the user chooses the view mode. This textfield allows comma separated entries of css classes
2. This entry results in a new media token element called "wrapper_class" that is inserted in the token with this data
3. These classes are then added to the, currently empty, wrapper div, allowing us to have very flexible layouts for these items. (the div currently at line 167 of media.filter.inc)

This seems like a simple fix to a potentially complex problem and gives us even more flexiblity in how we lay out these embedded fields. Here's a screenshot:

I can imagine that the argument against this approach may be that it's too complex for 'off the shelf users' who aren't modifying CSS. I agree that's probably the case, but it's potentially a powerful addition for advanced site builders while a 'plug and play' solution is underway and, once something more point and click is in place, this still has an added benefit of customizing more advanced layouts of embedded fields.