Clean up effect groups

[TomSnijders]

Currently there are a lot of effectGroups. See the manual, Section 18.2. These groups are for specific combinations of dependent and explanatory variables. They are used in function getEffects, which is defined in file effects.r. The combinations of effects and effectGroups are specified in allEffects.csv. It would be nice to clean up the tangle of effectGroups and treat the various combinations of dependent and explanatory variables in a more transparent way. This will require a reorganization of the code for getEffects and a redefinition of allEffects.csv as well as effectsDocumentation.r.