M101 - add description to mission exec abort events
M101 - Add descriptions to mission exec events

- also clean up the code a bit
Merge pull request #2138 from Bobfrat/abort_events

M101 - add description to mission executive events
M101 - Catch mission loader errors in mission_manager
Merge pull request #2140 from Bobfrat/mission-loader

M101 - Catch mission loader errors in mission_manager
NotificationSentEvent scanner plugin
notification worker reorganization
jinja/smtp added
cleaning up TODOs
persists Counter objects as standard dict