adding reducer for flagship sim

[hangqianjun]

Problem & Solution Description (including issue #)

Following examples in reducer.py I am adding a reducer for the Euclid flagship 2 simulation. This addresses #48.

Code Quality

• My code follows the code style of this project
• I have written unit tests or justified all instances of #pragma: no cover; in the case of a bugfix, a new test that breaks as a result of the bug has been added
• My code contains relevant comments and necessary documentation for future maintainers; the change is reflected in applicable demos/tutorials (with output cleared!) and added/updated docstrings use the NumPy docstring format
• Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[eacharles]

#48

[eacharles]

Thanks Qianjun!!