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.
bundle update
Specify Ruby 2.0.0 in Gemfile
Format
Rename @attributes to @attribute_names

Rename @attributes to @attribute_names and @<something>_attributes to @<something>_attribute_names.
Rename @.._associations to @.._associaiton_names
Do not use before_filter to simply find a record
Custom form builder: do not select among >15
Fix GuestEntry-MembershipPurchase association
Use strings instead of symbols for params keys

Use strings instead of symbols for params keys in MembersController and InstructorsController.
Edit controller tests
Add controller tests
Remove some comments
Remove 'strong_parameters' gem

Using custom functions to process parameters seems more reasonable and flexible.
Update ERD diagram
Start implementing params processing

Process attributes from params before using them for creating and updating records.

For now this is only done in MembersController, InstructorsController, and UsersController.

Leave TODO comments in other controllers.