LinkTaskManagers now have common parent class

Made all of the linkTaskManager* classes children of the LinkTaskManager
class, and starting moving common code to the parent.  Updated and renamed
ReplacementDict and ChoicesDict to be dicts (instead of having dicts as
attributes), and updated related code.  Moved code modifying a
ReplacementDict in a passVar to LinkTaskManager.
Preconfigured choices work for GetUserChoiceFromMicroserviceGeneratedList

refs #5874

checkForPreconfiguredXML checks if the description or anything in the
replacement dict matches the desired choice found in the processingMCP XML
file.  If it does, goes to that link, otherwise continues and requests user
input.