Modifications to elliptic eigenproblem example (#280)

* Add boundary condition switch

* Output eigenvalue absolute error

* Make eigenfunction sign in FOM and ROM consistent

* Clean up problems

* Change Gaussian radius

* Change calculation of Gaussian width

* Slight changes in example command lines

* Change filenames

* Remove TODO

* Astyle

* Change filenames. Change calculation of Gaussian width

* Slight changes to filenames

* Consistent sign over parameters and eigenvector ordering

* Astyle

* Fix visualization signs

* Fix stream names

* Reset stream name

* Reorganize reference mode sign logic

* Clean up

* Change variable names

* Warning meesages

* Astyle

* Normalize

* Adjust Gaussian

* Rename variables

* Remove verbose

* Update example in header

* Fix failing CI