Add Ability to Call "where()" with no Parameters

[jeffgbutler]

This will be useful for cases when there is complex logic associated with a where clause. A good example is seen in #100 where there is complex logic associated with creating a search and the where clause could be generated many different ways. We should support a usage like this:

QueryExpressionDSL<SelectModel>.QueryExpressionWhereBuilder builder = select(person.allColumns())
    .from(person)
    .where();

if (someCondition) {
  builder.and(id, isEqualto(3));
}

if (anotherCondition) {
  builder.and(firstName, isNull());
}

SelectStatementProvider selectStatement = builder.build().render(RenderingStrategy.MYBATIS3);

This should render properly regardless of whether all conditions, or none, are satisfied.