Continue message refactor, switch to Alire

[Eric-Edlund]

More work on refactor:

• I've done some work on Merc and updated some API files to match the refactor
• Tighter pre-conditions on sending messages

Switch project to Alire:

• This gives us access to the SPARK library

See commit history for details.

[Eric-Edlund]

Add fixing Jenkins to the list of things to do once this is merged to master