Do not allow querying of non-`Comparable` entity columns

[dmitrykuzmin]

Entity columns can be persisted in the storage as any Java type including non-Comparable ones.

When querying for column value, some implementations (for example, jdbc one) may require that column type is Comparable, and querying for non-Comparable columns makes little sense in general.

At the moment, the check that the column type is Comparable is performed during the query itself, failing it if the check does not pass.

We should handle the situation earlier, not allowing to query non-Comparable entity columns in the first place.

[alexander-yevsyukov]

@armiol, we could probably fail compilation when the column option is set on a non-Comparable type.

But I'm not quite sure why a column has to be Comparable, apart from the storage implementation argument.

Why cannot I have a column which only supports equality? I mean some values are not naturally sortable, e.g., phone numbers.