Upon request added extra default extensions

list of extensions using existing classes.
* = new extension

Using class="icon play"
.mp4
.mov*
.wmv*
.3gp*

Using class="icon audio"
.mp3
.wav*
.ogg*

Using class="icon worddoc"
.doc
.docx*

Using class="icon excelfile"
.xls
.xlsx*

Using class="icon ppt-file"
.ppt
.pptx*
Removed internal link icon from defaults

Seems people would like to define external as something which may have
several possible urls instead of just the one used by WordPress.
Therefor removed the internal link from the defaults. If you still need
it, the regex is:

/^$url/i

Replace the $url for your own url e.g. /^http://domain.ext/i