Relaxing BaseTable related visibility constraints

[alekmus]

We're using the data class based table definitions by subclassing the BaseTable class so we can write generics for the sql dsl. We are constantly running into the issue that the visibility of BaseTable related concepts is very restricted.

E.g making doBindInternal protected instead of internal would make extending the functionality easier/possible as it seems impossible to set _columns[key] values outside the library package, also making Column or/and ColumnBinding inheritable/delegatable would make working outside the Entity class a lot easier