Update card browser documentation

Because the menus have changed, need to update copy and imagery on this
page.
Change "Okay" to "Remove Now" on Stripper dialog

This helps clarify what the button does and makes it consistent with
others.
Improve messaging after stripping notes

Adds information about purging disused media files, and makes some
messages conditional.
Add accelerators for stripper radio buttons

This will make it quicker for heavy keyboard users to toggle the radio
buttons at the bottom of this dialog window.