Relative data paths should be handled in SIMPLib instead of the GUI

Unit tests are not passing because pipelines created with and for DREAM.3D that use relative paths are not compatible with any use of SIMPLib that does not use the GUI.

File path filter parameter widgets change the values of filter parameters so that only relative paths are saved but absolute paths are passed to the filter during preflight and execute. This creates divergent behavior between DREAM.3D pipelines and other projects that want to use the underlying SIMPLib library, like unit tests.