URL parameters preserved for attachment queries

[caronc]

Description:

This extends the attachment URL's to retain arguments that aren't used by Apprise. For example, to download something from dropbox, you'd need a URL like: https://www.dropbox.com/s/pu9ba7rhaierqqo/Avatar-sm.png?dl=1. Prior to this pull request, the dl=1 would become lost.

Parameter arguments are now preserved as long as they don't conflict with the ones Apprise uses (cache=, 'verify=, name=, and mime=).

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-io]

Codecov Report

Merging #187 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #187   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          71     71           
  Lines        8314   8323    +9     
  Branches     1330   1333    +3     
=====================================
+ Hits         8314   8323    +9

Impacted Files	Coverage Δ
apprise/attachment/AttachHTTP.py	100% <100%> (ø)	⬆️
apprise/attachment/AttachBase.py	100% <100%> (ø)	⬆️

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