Added selecting images and video at the same time

[askarsyzdykov]

Hi, @ParkSangGwon

Your project is awesome! I made this PR and hope you will merge it.
The purpose of this PR is:

• Closing the issue "choice both type (image+video)" choice both type (image+video) #117

And cleaning code:

• removed unused variables and methods;
• removed redundant initializations;
• removed empty lines;
• unified variables naming format;
• clean up xml files (removed commented blocks);