Extract setNextUrl

[eileenmcnaughton]

Overview

This code is repeated all over the task sub system. This is a first attempt to
extract it on the parent class in order to start consolidating it

Before

Code in main function & copied to many many places

After

Minor extraction to prepare for more cleanup

Technical Details

@monishdeb this is a follow on to the PR you merged - just about every task class seems to have a copy of this code & I think a lot of the nasty code on the task classes relates to it

Comments

[civibot]

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