updates to Graizer 18 GMM

See merge request !256

second attempt to implement, still incomplete. GMM enum included for testing in response spectra tool

Compute polygon area

Closes #145

See merge request !255

Fixed broken links

See merge request !254

Gulf coast margin zSed handlers and config updates

Closes #144 and #125

See merge request !253

Conditional spectrum (interim updates)

See merge request !252

Export updates

See merge request !251

Hazard export updates

Closes #140

See merge request !250

Sites fixes

Closes #140

See merge request !249

Graizer GMM

See merge request !237

Grid smoothing fix

See merge request !248

Updated code.json

See merge request !247

Removed unnecessary @Deprecated

See merge request !246

clean up for merge - comment out Gmm enum definition and test case. model is incomplete and requires feedback from author

more parts of graizer 18 model, with preliminary/placeholder (incorrect) test results. no basin term (need more info to implement), median ground motions are not reasonable at long periods.