Add rule class-signature

[paul-dingemans]

Description

Add rule class-signature. This rule rewrites the class header to a consistent format. In code style ktlint_official, super types are always wrapped to a separate line. In other code styles, super types are only wrapped in classes having multiple super types. Especially for code style ktlint_official the class headers are rewritten in a more consistent format.

Closes #875
Closes #1349

Checklist

Before submitting the PR, please check following (checks which are not relevant may be ignored):

• Commit message are well written. In addition to a short title, the commit message also explain why a change is made.
• At least one commit message contains a reference Closes #<xxx> or Fixes #<xxx> (replace<xxx> with issue number)
• Tests are added
• KtLint format has been applied on source code itself and violations are fixed
• CHANGELOG.md is updated
• PR description added

Documentation is updated. See difference between snapshot and release documentation

• Snapshot documentation in case documentation is to be released together with a code change
• Release documentation in case documentation is related to a released version of ktlint and has to be published as soon as the change is merged to master
• In case of adding a new rule, it needs to be added to experimental rules documentation