Feature/webapp visuals

[MaximeLecardonnel6x7]

Description

Changes to features importance plot x axis label and classification/regression display. Local explanation plot not displayed when no point or index selected.

Fixes
#428
#429
#430

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

Test Configuration:

• OS:Linux
• Python version:3.9
• Shapash version:2.2.2

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules