Add error handling/good fallbacks for Resource data

[brookslybrand]

Either add error messages/clear defaults when certain data doesn't load, or improve the error message shown. These are all the data fetching that needs to be handled:

• resources.yaml -- Can probably default to the main error page if this fails
• fetchReadme/getResourceReadme -- Individual resource page, show a message that the readme can't be loaded properly with a link to the repo
• image fails to fetch -- better fallback than a broken image
• getSponsorUrl -- Maybe just don't show the sponsor button if this one fails? I think this one actually works this way already
• fetchResourceGitHubData/getResourceGitHubData -- Maybe some good fallbacks, such as "failed to load description". I think this is better than the whole thing blowing up

[AlemTuzlak]

@brookslybrand for the broken images we could use the regex to possibly add an onerror attribute to link to a 404 image in the repo