refactoring and extending the support for FIFO and RR priority scheduling

• reworked the PriorityScheduler (FIFO)
• reworked the PriorityRoundRobinScheduler (RR) which now extends the PriorityScheduler with timeslicing and budgeting related features.
• added a new scheduler which extends the PriorityRoundRobinScheduler to offer both FIFO and RR scheduling policies that can be set per task.

requested review from @sreiser

assigned to @pourmohseni

changed target branch from master to develop

@pourmohseni I just discovered this nice feature to add a suggestion to fix things

You then can squash all of them together and push-force

added 4 commits

• 03dfbcf4 - minor fix to enable erasing an entry from the map and then return the...
• 565c1001 - refactored the PriorityScheduler to implement priority-based FIFO semantics...
• 21cfb578 - refactored the PriorityRoundRobinScheduler to derive from the...
• 45e95f53 - added a new scheduler which extends PriorityRoundRobinScheduler and offers...

Compare with previous version

I haven't checked it further, but if you can set the commit message, you can use the marvelous feature to use the keyword !fixup commithash for the new commit and afterwards you can do git rebase --autosquash. I think gitlab may help you with autocompletion of the commit hashes.

marked this merge request as ready

resolved all threads

mentioned in commit 7f253afe

merged