Apprise support for serialization via pickle library

[caronc]

Description:

Related issue (if applicable): #834

Added the ability to Pickle Apprise Objects

# e.g
import apprise
import pickle

# Instantiate our object
apobj = apprise.Apprise()

# Add our URLs
apobj.add("json://localhost")
apobj.add("xml://localhost")
apobj.add("form://localhost")
apobj.add("mailto://user:pass@localhost")

# Now serialize our object for any purpose
serialized  = pickle.dumps(apobj)

# We can re-load our object back into an Apprise Object
apobj2 = pickle.loads(serialized)

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

Testing

Anyone can help test this source code as follows:

# Create a virtual environment to work in as follows:
python3 -m venv apprise

# Change into our new directory
cd apprise

# Activate our virtual environment
source bin/activate

# Install the branch
pip install git+https://github.com/caronc/apprise.git@834-pickle-apprise

# launch python and try out the example above

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (de4701f) 99.52% compared to head (d1ebea9) 99.52%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #929   +/-   ##
=======================================
  Coverage   99.52%   99.52%           
=======================================
  Files         121      122    +1     
  Lines       16177    16250   +73     
  Branches     3312     3321    +9     
=======================================
+ Hits        16100    16173   +73     
  Misses         68       68           
  Partials        9        9           

Files Changed	Coverage Δ
apprise/Apprise.py	100.00% <100.00%> (ø)
apprise/AppriseLocale.py	100.00% <100.00%> (ø)
apprise/plugins/NotifyPushMe.py	100.00% <100.00%> (ø)

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