Added ability to change tooltip animate opacity.

[june07]

Proposed changes

Ability to change tooltip default opacity using options. The ultimate result are tooltips that can be transparent.

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.

[Smankusors]

Note: this PR has been merged to materializecss/materialize (materializecss#23)