Replace CompletableFuture with Promise

[whiskeysierra]

Detailed Description

https://github.com/vsilaev/tascalate-concurrent

Context

• Supports proper cancellation of tasks (incl. parent tasks)
• Supports interrupts
• Supports timeouts out of the box, making riptide-timeout obsolete
• Better support for composing futures

Possible Implementation

• Introduce dependency to https://github.com/vsilaev/tascalate-concurrent
• Replace CompletableFuture with Promise in APIs
• Replace CompletableFuture with CompletableTask in implementations

Your Environment

• Version used: 3.0.0-RC.0

[whiskeysierra]

Interrupts will become obsolete with #328. Timeouts are now already supported using Failsafe and no longer require a dedicated plugin/module. That leaves cancellations which are hopefully dealt with in #326. The remaining composition of futures/promises can already be done by wrapping/decorating/converting futures to promises within client code.

I'm closing this for now until new compelling reasons emerge.