front: Cleanup video plugin names, strings, credits for consistency.

Renamed our glide port "gles2glide64" to distinguish it from the
upstream version "gles2glide64mk2".  Also follows the current directory
name for the plugin and mirrors the naming of the other video ports in
the app, i.e. prefix with gles2 to indicate an OpenGL ES 2.0 port of an
original library.

Removed the credits for the plugins. Would be better to just post these
on the forum sticky where there's more room and we can link to upstream
sources, etc.

Updated the plugin version names to match what I *think* these plugins
are derived from.
glide: Wired up the stretch-screen option to the front-end menu.
front: Hide portrait-position preference when glide is used.

The option isn't available for that plugin yet, so we hide it from the
user to avoid confusion.