Revert "Use std::find to search observers"

This reverts commit c17b1dd1017433c17c6181f57d82235f49c2b239.

Refs #10377
Revert "Do not allow duplicate observers on an algorithm"

This reverts commit f6b01f277480cc07bff5ac71d500e7273588c53d.

Refs #10377
Do not clear the observer list

Refs #10377
Modify AlgorithmDialog to add observers just before execution

Refs #10377