Fix notify() failing when being called from an existing asynchronous event loop

[YoRyan]

Description:

Related issue (if applicable): #610

If an event loop is already in use, use it--instead of creating a new one, which fails with the high-level asyncio.run() function. Test included.

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• No lint errors (use flake8)
• 100% test coverage

[codecov-commenter]

Codecov Report

Merging #624 (314b5e6) into master (113fa36) will decrease coverage by 0.72%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##            master     #624      +/-   ##
===========================================
- Coverage   100.00%   99.27%   -0.73%     
===========================================
  Files          110      110              
  Lines        14266    14274       +8     
  Branches      2700     2700              
===========================================
- Hits         14266    14170      -96     
- Misses           0       91      +91     
- Partials         0       13      +13     

Impacted Files	Coverage Δ
apprise/Apprise.py	91.89% <100.00%> (-8.11%)	⬇️
apprise/py3compat/asyncio.py	100.00% <100.00%> (ø)
apprise/config/__init__.py	79.16% <0.00%> (-20.84%)	⬇️
apprise/conversion.py	91.78% <0.00%> (-8.22%)	⬇️
apprise/plugins/__init__.py	93.82% <0.00%> (-6.18%)	⬇️
apprise/URLBase.py	95.96% <0.00%> (-4.04%)	⬇️
apprise/plugins/NotifyFCM/color.py	96.66% <0.00%> (-3.34%)	⬇️
apprise/plugins/NotifySES.py	97.14% <0.00%> (-2.86%)	⬇️
apprise/plugins/NotifyFCM/priority.py	97.14% <0.00%> (-2.86%)	⬇️
... and 14 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 113fa36...314b5e6. Read the comment docs.

[caronc]

Thanks for the PR; looks like your code just doesn't handle Py36. Not sure if this merge request is even required after your great alternative solution you provided.

Is it worth adding this extra if/else section of code? Thoughts

[YoRyan]

Is it worth adding this extra if/else section of code? Thoughts

Well, it is a breakage - code that could previously call notify() from an async loop will no longer work. I suppose the merge/no merge question depends on how important you consider this kind of scenario.

[caronc]

Thanks for you quick reply. Your async knowledge is always so impressive. Would there be much needed to be compatible with py36?

[YoRyan]

Fixed! The test shouldn't have run with py36 in the first place, because it doesn't support asyncio.run().

(It's still not passing Travis because an unrelated test is failing. Looks like an external resource on outlook.com was not available.)

[caronc]

Thank you very much for all your great work!