tests: lib: table: Test all functions of the Table class.

Added unit tests for the Table class. All functions available by the
Table class are currently tested.
lib: table: Fixed errors in Table class found in the unit tests.

Fixed a lot of errors in the Table class which were found during the
unit tests for this class. Added a new size method which will return a
tuple of columns and lines. Added and hardened some argument checks in
the methods.