Identifier in schedule

[Yuki-Inoue]

Implements #753 , so, closes #753 .

With this PR, one can set identifier by writing following in the schedule.rb.

set :identifier, 'Some identifier'

If no identifier is given from commandline, this value will be used for the identifier; if one is given from commandline, commandline's value will be used.

If commandline does not give identifier and also not set in schedule.rb, then the default value of full path to schedule.rb will be used.

This PR includes #756 and #757 , so, closes #756 , and closes #757 .