BUGFIX detect mimetype of svg/js/css files using file extension

[weakbit]

The problem not detecting svg as svg+xml occured in php version 7.2.34 7.3.33 7.4.33

But not with 8.0.29 and 8.1.20 but i implemented the proposed solution anyway.

Also css/js files are now recognized by their file extension.

Shouls solve #85 #84