Add kill and relaunch feature

[mw98]

Just came across this workflow on Alfred's forum and I love how well thought out it is! Wanted to make some contributions:

1. Added a kill and relaunch feature in response to this comment on the forum.
   • Feature triggered by shift+return
2. Changed the output format from XML to JSON using the built-in json library.
   • Unfortunately this means dropping support for Alfred 2, but using JSON seems necessary for implementing this feature.
   • Unlike the JSON format, the XML format does not allow for item-specific workflow variables. Instead, it only seems to support one global variable per output.
     • While Alfred docs indicate that it should be able to support multiple variables, this seems to be broken, at least in v4.6.
     • It's unlikely to ever be fixed as the XML format has been deprecated.