Automatic refresh token

[bachya]

Describe what the PR does:

In order to more fully support the Home Assistant use case, this PR makes the following changes:

1. The library implemented no longer has to manually catch a TokenExpiredError and refresh the access token; that is done automatically.
2. Instead of a get_systems() method, the SimpliSafe object now provides class methods for instantiation via username/password or refresh token.

This is a breaking change. Read the documentation for new API usage.

Does this fix a specific issue?

N/A

Checklist:

• Confirm that one or more new tests is written for the new functionality.
• Update README.md with any new documentation.
• Run tests and ensure 100% code coverage: make coverage (after running make init)
• Ensure you have no linting errors: make lint (after running make init)
• Ensure you have no typed your code correctly: make typing (after running make init)
• Add yourself to AUTHORS.md.

[codecov]

Codecov Report

Merging #7 into dev will not change coverage.
The diff coverage is 100%.

@@         Coverage Diff         @@
##            dev     #7   +/-   ##
===================================
  Coverage   100%   100%           
===================================
  Files         5      5           
  Lines       241    247    +6     
===================================
+ Hits        241    247    +6

Impacted Files	Coverage Δ
simplipy/errors.py	100% <ø> (ø)	⬆️
simplipy/system.py	100% <100%> (ø)	⬆️
simplipy/api.py	100% <100%> (ø)

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