Glidedatetime folder issue fix (ServiceNowDevProgram#874)

* Rename GlideDateTime/readme to GlideDateTime/Get Date Difference/readme.md

Creating subfolder and moving corrected readme file into it.

* Rename GlideDateTime/GetDiffernceBtnDates.js to GlideDateTime/Get Date Difference/GetDiffernceBtnDates.js

Moving script file to new subfolder

Author: Lacah