ForeignKey Serialization

Implemented all the requirements for serializing and deserializing
ForeignKeys. This included removing the "linkedFkey" member variable
that was used to keep foreign keys in linking tables in sync. That value
is no longer stored and is recalculated when needed.
ColorRule Serialization 2

Added missing elements of ColorRule to be serialized.
Moved functionality for getting the attribute from a uuid into
FileManager from DataFile so you can access the attribute without
knowing the file to which is belongs.