Add image scraping support

[keenbed]

as per title

[dogwithakeyboard]

I put together a quick image yml scraper to test and it's not showing in my scraper list. I'm getting the following in the error log when reloading the scrapers:

Error loading scraper c:\stash\scrapers\TestImage.yml: yaml: unmarshal errors:
  line 10: field Title not found in type scraper.mappedImageScraperConfig
  line 11: field Date not found in type scraper.mappedImageScraperConfig
  line 22: field Details not found in type scraper.mappedImageScraperConfig
  line 23: field Photographer not found in type scraper.mappedImageScraperConfig
  line 24: field Code not found in type scraper.mappedImageScraperConfig

I'm assuming an image scraper would be almost identical to a gallery scraper and look something like this:

name: "Test Image"
imageByURL:
  - action: scrapeXPath
    url:
      - testurl.com
    scraper: imageScraper
xPathScrapers:
  imageScraper:
    image:
      Title: //title
      Date: 
        selector: //date
        postProcess:
          - parseDate: 2006-01-02
      Studio:
        Name: //studio
      Performers:
        Name: //performer
      Tags:
        Name: //tag
      Details: //details
      Photographer: //photographer
      Code: //title