Optimized merging wrt sections comparing, + another bunch of bug fixes

• pinger's current used section is checked before merging instead of all of what the pinger can ping since the unused ones will likely not be used anytime soon
• added code for reconciling pingers with default session (empty sessyr/sesscd) with their actual concrete sessions at the time of adding, for better merging
  • added pretty printing for session in coursedict in all modes
• fixed get_member sometimes None
• fixed reentering AddCourseDuration resulting in interaction failed due to same instance not being able to be used twice
• fixed search mode error when session is missing
• fixed incorrect results due to wrong timespan parameter keys naming
• fixed wrong indentation on sleep in pinger that resulted in unnecessary cooldowns between pinging multiple users