Add keyword to get response from last request

[PaulBrandUWV]

This Pull request adds a keyword to get the response from the last request.
The keyword can be used to create much cleaner testcases because the response does not have to be stored to a variable in the test case.

Example:

*** Settings ***
Library     RequestsLibrary

*** Variables ***
${url}    https://httpbin.org/base64
${data}    anlmhcrh7853r042yqtx7rhaohfx,jr0aofds*&*^$IHLFEMXhkdjsxhcc
${base64_data}    YW5sbWhjcmg3ODUzcjA0MnlxdHg3cmhhb2hmeCxqcjBhb2ZkcyomKl4kSUhMRkVNWGhrZGpzeGhjYw==

*** Keywords ***
Response body equals
    [Arguments]    ${data}
    ${response}=   Get response
    Should be equal    ${response.text}    ${data}

*** Test cases ***
httpbin base64 decode
    When get  ${url}/${base64_data}
    Then response body equals    ${data}

This PR also removes some skipif decorators from the unit tests for old python versions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.93%. Comparing base (6899855) to head (ea64dd3).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #397      +/-   ##
==========================================
+ Coverage   85.29%   88.93%   +3.64%     
==========================================
  Files           9        9              
  Lines         476      479       +3     
  Branches       49       49              
==========================================
+ Hits          406      426      +20     
+ Misses         65       51      -14     
+ Partials        5        2       -3     

Flag	Coverage Δ
acceptance	85.38% <100.00%> (+0.09%)	⬆️
unit	60.12% <66.66%> (?)

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[PaulBrandUWV]

@lucagiove what do you think?

[lucagiove]

It's an interesting keyword I'm wondering whether the name of the keyword might be more clear, maybe something like "Last Response" ? It's a concept that already exist in the code.
Also because get might be confused with GET http method.

[PaulBrandUWV]

Makes sense! I renamed the keyword. The class method can not be "last_response" since that name already exists in scope.

[PaulBrandUWV]

Thanks!