added onMouseEnter property to frost scroll

[helrac]

issue #496

• [ ] #none# - documentation fixes and/or test additions
• [x] #patch# - backwards-compatible bug fix
• [ ] #minor# - adding functionality in a backwards-compatible manner
• [ ] #major# - incompatible API change

CHANGELOG

• Added an optional mouseenter event for the ps-container to update which can then remove or add scrollbars

[rox163]

:+1: