added sign_in_count and last_sign_in_at columns to users model
added default timezone configuration in application.rb
configured config.time_zone and config.active_record.default_timezone ALL to :utc
set all environment timezone to utc
deleted time settings in application.rb
using 'UTC' as timezone setting in application.rb
using :utc for config.active_record.default_timezone
Merge branch 'user-activity-tracking'