Mike 1263 multiclass plot bug

[mmastand]

User now has control of:

• Text size within confusion matrix tiles (or turn off)
• Angle of x axis text

Size defaults to 3, which is usually readable. Angle to 60 degrees. Tests and docs done.

[codecov[bot]]

Codecov Report

Merging #1269 into master will decrease coverage by 0.1%. The diff coverage is 77.7%.

@@           Coverage Diff            @@
##           master   #1269     +/-   ##
========================================
- Coverage    95.3%   95.2%   -0.2%     
========================================
  Files          40      40             
  Lines        3125    3140     +15     
========================================
+ Hits         2980    2991     +11     
- Misses        145     149      +4