Add RootedTree TryReplaceEdge error control

[cmwedin]

from the sprint 1 review:

"A change will need to be made to the TryReplaceEdge method to prevent a multiple roots, but this bay be a complicated change. The issue when swapping the nodes on an edge, some of the edge replacements will break the condition of a rooted tree, but in the end the new graph will rectify it. However, if we restricted TryReplaceEdge from ever breaking the condition of a rooted tree then those individual swaps would not be able to be preformed as the AbstractEdge.TrySwapNodes() method uses TryReplaceEdge toreplace each of the preswap edges with the new edges one by one. A potential solution to this would be to move TrySwapNodes from the AbstractEdge class to the AbstractGraph class and decouple it from the TryReplaceEdge method, similar to how the TryReplaceEdge method was introduced to decouple removing and replacing an edge from the TryAddEdge and RemoveEdge methods."