Added tests for the DeletionTool.
Some tweaking of the creation logic behind the tools.
Now when setSelected() gets called, the method checks to make sure the entity isn't null, thus preventing NPEs under certain circumstances.
CellTool gets passed in from outside rather than being created by the class itself.
build() gets the ConnectionType from the passed-in Cell rather than trying to figure it out itself.
Constructor now takes tools passed-in from outside rather than creating tools for itself.
Made some updates to the tests to account for changes made to the classes under test.