fix css validation logging + refactor code

[lordlabuckdas]

• end_time being calculated in the finally part of the block guarantees that printing elapsed time will not error out due its non-initialization. This however increases the end time (though by an insignificant amount) due to cloner shutting down.
• Improved output formatting issues with the spinner animation.
• Cloner shows CSS validation despite it being disabled by default. This was because CSS validation was set to use the default logger. This PR makes sure that all CSS validation is sent to the logs and disables it if set to False.
• With this PR, the presence of the --css-validate flag enables CSS validation and does not require the user to enter "true" or "false" after it.
• itr, used as the index of the spinner animation, will now never exceed len(animation)-1