Allow defining verbosity

[zaimramlan]

Background:

• This gem uses the jquery.periodicalupdater.js plugin.
• In jquery.periodicalupdater.js, verbose allows developer to see the error logs through the developer console of a browser.
• The values that the verbose attribute accepts are:
• 0 = none
• 1 = some
• 2 = all
  Reference:
  https://github.com/RobertFischer/JQuery-PeriodicalUpdater/blob/master/jquery.periodicalupdater.js

  Changes:

• Instead of forcing a definite value of verbose: 2, it is better to change it to be definable by developers who use this gem.
• Developers may now change the value of verbose, to limit the logs that will be displayed in the Developer's Console.
• Also, these logs should only be displayed in a development environment, instead of the production environment, where end users may also see.