Avoid repetitions in Accessors module

Use meta-programming to avoid repetitions in Accessors module.
Simplify MembersController with meta-programming
Simplify RegisterController
Clean up
Change filtering

Use new classes SimpleRelationFilter and FriendlyRelationFilter and a new ApplicationController private method #do_filtering, instead of including a filtering module into all models,
Work on PseudoColumns module and its use
Extend PseudoColumns to remember column names

Extend the PseudoColumns module to remember column names as strings.

Attention: the instance variable @column_names already exists in ActiveRecord.  Added variable is called @pseudo_column_names.
Format
Change sorting

Similarly to filtering, make the controller responsible for sorting.  Do not mix in Sorting module into models, remove it completely.