Use fast version of easy-bf instead of current

There are two versions of easy-bf in the original project batsched:

• easy-bf meant to be simple and hackable, but slow. That's the one currently used in batmen
• easy-bf-fast meant to be fast but less hackable

We are currently running into problems where easy-bf execution time explodes, so it might be wise to change to the second implementation...

TODO

• add easy-bf-fast in the list of schedulers
• adapt it to Dynsched
• add the way to create a new Dynsched in the doc: #7 (closed)
• test that it behaves the same as easy-bf
• delete easy-bf and replace it with easy-bf-fast