When a person has set up "Working Hours", use those hours instead of 9-6 in their time zone

[flavorjones]

Today, we use these settings to determine the working hours in which to book a meeting:

# lib/calendar_assistant/config.rb
      Keys::Settings::START_OF_DAY => "9am",              # BusinessTime
      Keys::Settings::END_OF_DAY => "6pm",                # BusinessTime

When a person has set up "working hours", though, we should use those hours (in their time zone, natch) instead of 9-6.