Modify Mass Rename Script for More General Image Formats

[zacharycwillson]

mass_rename.sh only successfully executes with images saved as lowercase .jpg extension. Script should be modified to accept images regardless of extension case or format (i.e. .jpeg, .JPEG, .JPG). Script should be modified to prompt user for desired file extension and accept input as an argument. @aewhite100

[zacharycwillson]

Script is modified to accept any file extension as an argument and rename all files in the specified directory that fit provided input. Failure due to extension case is resolved @aewhite100