Change the dropdown selection to something more user-friendly for larger volumes of options

Right now we're only listing ~80 identity providers, so the drop-down list is still fine for now.
However, we would like to allow identity providers from the inter-federation to be listed as well, which number in the thousands.

For this, a simple drop-down list will of course not suffice anymore and we will need support for search-as-you-type/typeahead.

• Replace the drop-down list with a combo-box
• Add search-as-you-type/typeahead support
• Display IdP logos for each option in the selection list