Built most of the ImtLinkGrpSet class, which manages a set of ImtLinkGrp objects. This involved making some modifications to ImtLinkGrp, so that it is aware of the possible existence of its parent object and is able to add and delete itself in the parent where appropriate.

Lots of work still to do on this class, much of which will require that I do more detailed planning on how exactly it will interact with the ImtDoc object. I need to thoroughly test the readFromDomElement() function, and add functions such as getLinksForZone(), getLinksForTextEl(), and getters and setters for all the relevant members of ImtLinkGrp and ImtLink.