New implementation centered around SObjectRepository.cls

Refactored again - core logic lives in the abstract class SObjectRepository & interface ISObjectRepository

• SObjectRepository uses field sets in the constructor and has several protected builder methods. These are used to give a structured method of building a query string
• Class constructors can be overloaded to allow a field set to passed in
• By default, some the common query fields are automatically added to the query. This includes audit fields (created by ID/created date, etc), name/subject fields, and a few other similar fields. A boolean can be passed to disable this
• Any queries needed in your codebase should be packaged as public methods. These should call any private/protected builder methods and return the results of the query, casted to the appropriate data type
• Two example concrete classes are included - LeadRepository.cls & TaskRepository.cls
• Two utils classes, CollectionUtils & StringUtils, are also included