MediaSearch's filters mimeType, imageSize & license map directly to Cirrus search keywords filemime, fileres and haslicense.
I suggest we simply use the same keywords:

• it saves some code & complexity from mapping one thing to another and back
• it's more straightforward for those who know and use these keywords already

Note: I think it'd also make sense to map type to filetype, although that one's slightly special because - for the categories&pages tab - it doesn't map to a cirrus keyword, but kicks off another type of search altogether. (out of scope for this ticket)

Acceptance criteria:

• the URL query param for licenses becomes haslicense
• the URL query param for file types becomes filemime
• the URL query param for images sizes becomes fileres