Reworked the table class to accept string columns for ticket #601
Resolved two minor issues in implementation of #601
Code for ticket #601 now compiles again.
Backup commit for ticket #601 -> file.cpp can be compiled now -> Reduced the number of orphane ToDos in code
Backup commit for ticket #601
Improved implementation of #601 Added the table column headlines to the copy and assign methods.
Resolved even more compiler errors for ticket #601
Reduced the number of warnings and resolved some ToDos for ticket #601
Fixed many compiler errors for ticket #601