Make use of recipe-scrapers for web imports

[cydanil]

Description

This PR aims to deprecate existing web importer plugins and replace them with a single unified importer leveraging recipe-scrapers, as described in #18 .

This MR is rather large and part 1 of the implementation: the functionality works as intended, but user feedback is lacking.
The import UI was reworked in a single dialog for web and file imports by introducing a URIDialog class.

All previous web importers were deleted.

How Has This Been Tested?

This was tested by importing web and file recipes.
A basic integration test was added.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[lgtm-com]

This pull request fixes 28 alerts when merging 096a581 into 5719ba1 - view on LGTM.com

fixed alerts:

• 11 for Incomplete URL substring sanitization
• 6 for Except block handles 'BaseException'
• 6 for Unused import
• 1 for Testing equality to None
• 1 for Unused local variable
• 1 for Module-level cyclic import
• 1 for Use of 'global' at module level
• 1 for `__init__` method calls overridden method

[cydanil]

I'll merge this, and address the failing CI in the next MR in order to make the changes more readable.