Added local task registry, improved shared_tasks API.

[s3rius]

As discussed with @dtatarkin in #202 we need to have a difference between tasks registered by user and shared, that were created using async_shared_broker.

[dtatarkin]

Thank you very much, this solution works well for me!

[codecov-commenter]

Codecov Report

Merging #203 (98240e2) into develop (e66f3aa) will increase coverage by 4.93%.
Report is 115 commits behind head on develop.
The diff coverage is 71.83%.

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@@             Coverage Diff             @@
##           develop     #203      +/-   ##
===========================================
+ Coverage    67.62%   72.55%   +4.93%     
===========================================
  Files           37       45       +8     
  Lines          942     1472     +530     
===========================================
+ Hits           637     1068     +431     
- Misses         305      404      +99     

Files Changed	Coverage Δ
taskiq/abc/middleware.py	100.00% <ø> (ø)
taskiq/abc/result_backend.py	100.00% <ø> (ø)
taskiq/cli/watcher.py	0.00% <ø> (ø)
taskiq/cli/worker/log_collector.py	100.00% <ø> (ø)
taskiq/cli/worker/process_manager.py	0.00% <0.00%> (ø)
taskiq/cli/worker/run.py	0.00% <0.00%> (ø)
taskiq/events.py	100.00% <ø> (ø)
taskiq/result/v1.py	0.00% <0.00%> (ø)
taskiq/result_backends/dummy.py	100.00% <ø> (ø)
taskiq/brokers/zmq_broker.py	44.73% <27.27%> (+4.19%)	⬆️
... and 28 more

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