[FIX] Scatterplot: Disable vizrank when features on input

[VesnaT]

Issue

Feature selection is enabled, even though features are passed to the input of Scatterplot.
To reproduce: File (Iris) -> Scatterplot
-> Correlations -> Scatterplot -> Axis x, Axis y and Find Informative Projections are enabled

Similar to #4101.

Description of changes

• disable table and button on vizrank popup when features are not the input of the widget
• disable attr_x and attr_y selection when features are not the input of the widget
• initialize vizrank only when data (input) changes, not features

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #4102 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4102      +/-   ##
==========================================
+ Coverage   85.56%   85.57%   +<.01%     
==========================================
  Files         385      385              
  Lines       69201    69215      +14     
==========================================
+ Hits        59211    59229      +18     
+ Misses       9990     9986       -4