Refactor base class to be service-agnostic

[supremebeing7]

Eventually, the gem should ask the user which services to integrate. For now, the base class TimeLogRobot makes calls to Toggl::Report and JIRA::WorkLogger, which is not great. The calls instead should be made to non-namespaced services, which then inspect some param/argument and route to the proper service accordingly. See the Entry and Tagger models for examples.