Support visualizing heterogeneous tables

[Reemh]

So far those tables cannot be visualized as a heatmap.

• Option 1: visualize them using the table visualization from Caleydo --> too much details for really large tables but this is what already is supported from Caledyo.
• Option 2: visualize them as a heatmap --> this requires normalizing all the values, with regards to each column data type, to values between 0 and 1. Also it might be using a different heatmap implementation than the one already available from Caleydo.
• Option 3: find a different meaningful table visualization --> implement this visualization.

[thinkh]

Obsolete, because we agreed on homogeneous tables.