Configurable scraper user agent string

[WithoutPants]

Replacement PR for #346 since I didn't want to push to the develop branch of @hiddenpants255 repo.

Adds a user agent string configuration option. This user agent string is applied for all http scrape requests.

I've also added an option in the scraper config to print the returned html response in the log. To enable it, add the following to the scraper yml file:

debug:
  printHTML: true

Can be tested with hotguysf**k website. If the agent is not set, then the page is not loaded due to WAF. Setting the agent string to a valid browser results in the correct response. Here is an example config (I have censored the url and title in case of github moderation):

name: Hot Guys F**k
sceneByURL:
  - action: scrapeXPath
    url:
      - hotguysf**k.com
    scraper: sceneScraper
xPathScrapers:
  sceneScraper:
    common:
      $performer: //div[@class='content-meta']/h4[@class='models']/a
    scene:
      Title: //div[@class='videoTitleIntro']/h1
      Details: //div[@class='descriptionIntro']/p
      Date:
        selector: //div[@class='introDatePublished']
        replace:
          - regex: (st|nd|rd|th)
            with:
        parseDate: Jan 02,2006
      Image:
        selector: //div[@class='videoPoster']//img/@src