Unify symbols in get/set manopt parameters.

[kellertuer]

This was indeed less of changes than I thought, but it finishes two of the points on the 1.0 Roadmap.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.77%. Comparing base (1856a26) to head (ad0d9b8).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #383 +/- ## ========================================== + Coverage 99.54% 99.77% +0.23% ========================================== Files 73 73 Lines 6981 7243 +262 ========================================== + Hits 6949 7227 +278 + Misses 32 16 -16 ```

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