Add multithreading to link checking; and other improvements

Add multithreading to link checking; and other improvements

• Add multithreading to link checking -> self.assert_no_404_errors() now works faster
• Add pytest-ordering
• Fix method that calculates full links from partial links
• Add slow-scrolling to demo_mode asserts
• Add Swag Labs test suite to the examples

Update Firefox profile settings and urllib3 version

• Update Firefox profile settings
• Update urllib3 version

Update pytest version to 4.4.1

Update pytest version to 4.4.1

Several minor updates

Several minor updates:

• Screenshots update
• Parameter update
• .gitignore update
• utf-8 encoding
• Docs update

Add ability to save page elements as screenshot files

Add ability to save page elements as screenshot files

Disable pytest's cacheprovider plugin

Disable pytest's cacheprovider plugin

Updates: Chrome log-level, pytest libs, Azure pipelines

Some minor updates:

• Use log-level 3 for default Chrome logging
• Use pytest-forked>=1.0.2
• Update Azure test pipeline

Update test reports

Update test reports

• Some changes to the way screenshots are saved for the reports

Allow passing a boolean value to desired capabilities

Allow passing a boolean value to desired capabilities

• All formats as of now:
  'KEY': 'VALUE'
'KEY': True
'KEY': False
caps['KEY'] = "VALUE"
caps['KEY'] = True
caps['KEY'] = False
  (Each pair must be on a separate line. You can interchange single and double quotes.)
  See https://github.com/seleniumbase/SeleniumBase/tree/master/examples/capabilities for the full ReadMe and sample capabilities files.

Refactor visual/layout testing

Refactor visual/layout testing