fix(options)!: default values and validations from the get go

[aleksasiriski]

• [x] Both CLI and HTTP mode have all the options set with defaults and are validated (so no need to check again in colly prepare), and now options aren't being changed (so no need to pass as pointer)
• [x] BREAKING: Removed some options
  • JustFirstPage (wasn't being used anywhere)
  • Mobile (only Qwant supported it and could compromise privacy if it's not the same for all users)
  • User Agent (if users set a wrong one a server could easily get it's IP banned, also it compromises users privacy if it differs from other users)