Support multiple API keys per service

[TheTechromancer]

Addresses #1601.

TODO:

• Add support for multiple API keys per module
• Tests for multiple API keys
• Tests for multiple API keys + api_page_iter
• Tests for failed_request_abort_threshold

[codecov]

Codecov Report

Attention: Patch coverage is 96.78363% with 11 lines in your changes missing coverage. Please review.

Project coverage is 93%. Comparing base (3b52525) to head (a2125c4).
Report is 19 commits behind head on dev.

Files with missing lines	Patch %	Lines
bbot/modules/base.py	91%	8 Missing ⚠️
bbot/modules/templates/github.py	93%	1 Missing ⚠️
bbot/modules/templates/shodan.py	92%	1 Missing ⚠️
bbot/modules/templates/subdomain_enum.py	50%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             dev   #1810    +/-   ##
======================================
+ Coverage     93%     93%    +1%     
======================================
  Files        346     346            
  Lines      26847   27058   +211     
======================================
+ Hits       24752   24970   +218     
+ Misses      2095    2088     -7     

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