Allow timepicker container to be an element

[Cerothen]

Proposed changes

The datepicker requires an element to be specified for the container, the time picker requires a selector string. This change allows an element to be specified while retaining the original method as a fallback

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to change).

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[Huluti]

Hi! You shoud probably propose this change in this active fork: https://github.com/materializecss/materialize