Lookup fixes + minor changes

1. Table.load now properly subclassess the table instead of always resulting in tablite.Table.
2. Table.from_* methods now respect subclassess, fixed some from_* methods which were instance methods and not class methods.
3. Fixed Table.from_dict only accepting list and tuple but not tablite.Column which is an equally valid type.
4. Fix lookup parity in single process and multiple process outputs.
5. Fix an issue with multiprocess lookup where no matches would throw instead of producing None.
6. Fix an issue with filtering an empty table.