escape quotes in dropped filenames

[snoyer]

OnDropFiles() needs to escape quotes in filenames before adding quotes around them.
Also TriggerBinding() should add a space between commands and first argument instead of expecting said space to be there already.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.96%. Comparing base (78ff702) to head (6dd3296).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1725   +/-   ##
=======================================
  Coverage   96.96%   96.96%           
=======================================
  Files         108      108           
  Lines        8792     8805   +13     
=======================================
+ Hits         8525     8538   +13     
  Misses        267      267           

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[mwestphal]

Ideally a test using a file with a name withs spaces should be added/modified into, but I can take care of it if needed.

[mwestphal]

superseeded by #1728