Speaker role improvements

Problem/Motivation

Based on the current configuration, there are some things that can be confusing for users of an Event Platform site:
- Speakers may not have permission to use the text format allowed for their bios
- Speakers can't edit their session after it's submitted (tabs don't show)
- When speakers do update their session, it becomes unpublished (probably a workflow issue)
- All users get the speaker role, even if their session hasn't been accepted or they don't need it. This prevents using the role as a way to differentiate, for example in views or when pulling lists

Proposed resolution

Update the configuration to resolve the cited issues. It may also be worth investigating an option other than the Registration Role module (such as Profile, or potentially ECA) to control how and when the role is assigned.