Margin-Extension

Calculate Margin, has pre-defined values 10,15,20,25,30,35,40% or you can enter a custom margin percentage value. Any bugs or improvements please let me know and I will try improve it as it's my first extension i have made while learning to code. Update 1.1 - Updated Package name so it's changed in the Chrome Store Update 1.2 - Added error checking,make sure only ints are used in the user input. Error message added if any non INT characters are used.