Allow admins to upload hero images for the site through an admin

[Cara-Jo]

Instead of having images for the headers (hero images) be static, let's find a way to have admins upload images through the admin.

Acceptance criteria:

• Create a page for admins to upload hero images.
• Create a way for admins to crop images to a specific aspect ratio after upload.
• New image appears on the selected pages.

[westonplatter]

@Cara-Jo for some reason this popped up on github for me today. Do you have a desired storage backend? For example, google drive, AWS s3, etc? I'd suggest google drive since we could probably rig this up for free (using AWS = 💰).

One of many possible ways of doing this, would be to use https://github.com/tors/jquery-fileupload-rails to handle the upload, cropping, and saving in tandem with either Paperclip or Carrierwave.

[Roenok]

@westonplatter The site already supports image upload; we use it for chapter leader headshots and sponsor logos.

In general, though, I don't think there is much need for this feature. We have not ever changed the hero image in many years of using the site. If we need to change it at some point, it would be a very small pull request.