Removes Flurl dependency

[Psypher9]

Description

This PR addresses issue #92 and removes the need for Flurl as a dependency.

This is only meant to be an intermediate solution before simplifying the way query strings are generated with ListRequestOptions. See #91 for more information

Purpose

• Bugfix (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

• I have added tests to prove that what I have fixed or added does indeed work
• I have added documentation as necessary

[radek-petrik-se]

I suggest rollback for this merge/pull request. For removing the Flurl dependency just replace the SetQueryParam extension with own implementation of the same functionality. It will be easier to maintain and also fix errors like missing escaping, missing ampersands, etc. . I have marked just one example of missing ampersand in the commit 5a4f646, but there are many more.