[Bug] Tooltips when using hexbin binning not customizable

**Describe the bug**
When creating a hexbin visual, and setting the `color` and `height` attributes by one (or more) of the columns, the tooltip displays by default both on the tooltip, even if the the two fields are affected from the same column (see screenshot).

**To Reproduce**
Steps to reproduce the behavior:
1. Create a visual with hexbins
2. Change the `height` and the `color` to be defined by the same column.
3. Enable the tooltip with any field
4. Hover over the data and see the issue.

**Expected behavior**
When using the same column to define both attributes, the tooltip should only display one. Alternatively, allow the user to decide which one they would like to show on the tooltip (better alternative).

**Screenshots**

**Desktop (please complete the following information):**
- OS: Win10 Home
- Browser Chrome 76
- Version 1.1.3