CLI: print a message when 0 shots has been exported

[andersonjoseph]

Shotbit CLI should display a message when it couldn't find any shot to export,

Something like:

I could not find any shots to export in this video. Try to:
increase '--similarityTreshold'
or reduce '--minLength' 

A possible way to do this is returning an array containing the shots path on the shotsExported event so in CLI we could just listen for this event and then check for array.length > 0