Separate TransferHandler and Taskers

Server side

Add 3 interfaces:

• PreTasker
• PostTasker
• ErrorTasker

Responsible to run the respective tasks list. Remove those function from TransferHandler. When the tasks should be run, check if the TransferHandler is a Tasker (Ex: is the TransferHandler a PreTasker at Request validation). If it is then run the tasks. If not pursue transfer.