[ENH] OWCorrelations: Data info displayed in the status bar

[aturanjanin]

Description of changes

Input/output data info displayed in the status bar.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #4455 into master will decrease coverage by 4.29%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4455      +/-   ##
==========================================
- Coverage   87.46%   83.16%    -4.3%     
==========================================
  Files         405      268     -137     
  Lines       74128    53997   -20131     
==========================================
- Hits        64836    44907   -19929     
+ Misses       9292     9090     -202

[VesnaT]

Info is not updated with one instance on the input.

[VesnaT]

This it not correct info when self.cont_data is None and self.data is not None.

[VesnaT]

To avoid duplicated code, I'd suggest removing upper to lines and add something like:

    def commit(self):
        self.Outputs.data.send(self.data)
        summary = len(self.data) if self.data else self.info.NoOutput
        detail = format_summary_details(self.data) if self.data else ""
        self.info.set_output_summary(summary, detail)

        if self.data is None or self.cont_data is None:
            self.Outputs.features.send(None)
            self.Outputs.correlations.send(None)
            return

at the beginning of the function.