Update favicon to include PNGs and remove shortcut from link rels

DQT should be checked to make sure that PNGs are included for favicons and the [shortcut link type](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Attributes/rel) removed from the `rel` attribute.  See also https://github.com/ThreeSixtyGiving/qualitydashboard/issues/36#issuecomment-4397663584