Improved element#add/remove/hasClass methods.
Fixed incorrect addClass usage.
API docs: Minor improvement.
Reverted incorrect change made in #3679.
Code refactoring: Reused the hasClass code which does not create regexp patterns for every class.
Fixed more incorrect addClass usage.
Tests: Improved test cases names.
Tests: Added missing tests for element.hasClass.
Changelog entry.
Merge branch 't/10903b' into major