Rename the blockly icon CSS classes to use camelCase

[BeksOmega]

Rename the following CSS classes and references to them:

• .blockly-icon-comment -> blocklyCommentIcon
• .blockly-icon-warning -> blocklyWarningIcon
• .blockly-icon-mutator -> blocklyMutatorIcon

This change should be made against the rc/v12.0.0 branch. This should be marked as a breaking change.

To work on this issue, comment below asking to be assigned.

[ga-fleury]

Hey @BeksOmega, I'd like to work on this

[BeksOmega]

Sweet, thanks for the comment @ga-fleury =)