OWTable: remove color palette selection
OWTable: remove color palette selection

The user doesn't select their color palette. If they do, they may
have to re-do it for every widget that supports it. They probably
don't.

If _visualize continuous values_ and _color by instance classes_
were true, the widget crashed on data tables with
`len(class_var.values) > len(colors in palette)`. An example is
audiology.tab dataset with a new continuous feature constructed
(e.g. `sqrt(speech) + sqrt(air) + sqrt(ar_u)`).

This patch prevents user's choice and solves the crash by setting
the perfect color palette for each dataset.

Allowing to opt for a particular color palette, as a pure
convenience to the user, should be done globally and elsewhere.

qPCR4vir/orange3,cheral/orange3,cheral/orange3,marinkaz/orange3,marinkaz/orange3,marinkaz/orange3,marinkaz/orange3,kwikadi/orange3,qPCR4vir/orange3,kwikadi/orange3,qPCR4vir/orange3,qPCR4vir/orange3,qPCR4vir/orange3,kwikadi/orange3,cheral/orange3,kwikadi/orange3,cheral/orange3,marinkaz/orange3,kwikadi/orange3,kwikadi/orange3,marinkaz/orange3,cheral/orange3,qPCR4vir/orange3,cheral/orange3