Message passing with more information

[unkcpz]

• Simplipy _create_state_instance so it only need to do real object creation.
• Killed state message is a message type
• Make message not global variable and able to attach with more information.
• pause/play/state all using build method to build the message.

[unkcpz]

A lot of single quotes to double quotes changes came from my IDE linter, should be reduced if #289 get merged and this PR will contains much less line changes.

[codecov]

Codecov Report

Attention: Patch coverage is 86.85714% with 23 lines in your changes missing coverage. Please review.

Project coverage is 90.77%. Comparing base (14b7c1a) to head (96c5842).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/plumpy/processes.py	78.95%	8 Missing ⚠️
src/plumpy/event_helper.py	0.00%	2 Missing ⚠️
src/plumpy/ports.py	85.72%	2 Missing ⚠️
src/plumpy/process_comms.py	90.00%	2 Missing ⚠️
src/plumpy/process_states.py	89.48%	2 Missing ⚠️
src/plumpy/base/state_machine.py	96.30%	1 Missing ⚠️
src/plumpy/communications.py	75.00%	1 Missing ⚠️
src/plumpy/events.py	75.00%	1 Missing ⚠️
src/plumpy/persistence.py	85.72%	1 Missing ⚠️
src/plumpy/process_listener.py	0.00%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #291   +/-   ##
=======================================
  Coverage   90.77%   90.77%           
=======================================
  Files          22       22           
  Lines        2990     2990           
=======================================
  Hits         2714     2714           
  Misses        276      276           

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