error and warning handling

[bradfordcondon]

Errors vs exiting etc is handled inconsistently. Convert all print/exit statements to warnigns provided by the importer class:

see https://tripal.readthedocs.io/en/latest/dev_guide/custom_data_loader.html?highlight=warnings

[almasaeed2010]

did we fix this for test suite?

[bradfordcondon]

short story, this is a core problem.
tripal/tripal#588

i think that i started working on it but didnt see the point with how its currently set up.

[bradfordcondon]

• no exits in expression loader/biomaterial loader

We still use print though, especially in hte expression loader. the biomaterial loader has most messages changed to API calls like so:

      tripal_report_error('tripal_biomaterial_loader', TRIPAL_ERROR, $message, ['!path' => $file_path], ['print' => TRUE]);

I'm not sure why we're doing that instead of using $this->logMessage()?