Add ability for organisers to contact chapter members directly from the admin section of the codebar website

There have been a number of requests recently from organisers wanting to contact their chapter members by email. Organisers have access to chapter member emails and the only way for them to contact members is for them to use these email addresses manually. This has a couple of problems:

• Organisers have access to email addresses. It would be good to minimise this.
• There is a risk of accidentally using cc rather than bcc and thereby exposing the email addresses.
• They have to use their personal email accounts for "official" emails which might end up in spam.
• Only three levels of granularity: all coaches/students in the chapter, everyone that attended a specific workshop, individual member.

It would be good to have the ability to email members from within the codebar web interface without having to manually deal with email addresses. It's unclear what the minimum functionality should be for this, given the differences in chapter sizes and varying needs. Based on my own personal experience, the types of email I have sent the most are to attendees of a specific workshop to give them last minute updates.

Meetup has an interface for sending emails that might be useful for inspiration. It allows sending emails to varying subsets of a group.

Start in the admin section of the codebar website and review how chapter members, workshops, and organisers are represented. Clarify the minimum recipient-selection and email requirements with maintainers before implementation. Done should be a defined, reviewed way for organisers to contact the intended members without manually handling addresses.