Limit which speakers are listed on the speaker page

[drnlm]

When using talk types for several different events, one may not want the submitters for all the types to show up on the speakers page.

For instance, PyConZA uses talk types for Open Space topics and Demos, and the submitters of these should probably not be grouped with the other speakers.

Organising the speakers page by type. instead of purely alphabetically, might also be an option worth looking at.