Simplify the general config screen somewhat by getting rid of the dropdown box of external browsers, and just puting the custom browser text edit there instead.

This makes sense as we cannot possible keep up to date with all browsers on Linux, Win and Mac, which would lead many people to use the text edit in any case.

This also makes the config dialog a little bit less tall.
Oh, an Amarok actually saves this setting now, thus closing the bug! :-)