Add css striping to mark duplicate files together

Problem/Motivation

It would be nice to have css color striping for the groups of duplicate file. E.g. white / light grey background color for the rows with the same checksums. This would let there be a visual way to see how many files are the same.

Steps to reproduce

N/a

Proposed resolution

• Use a class an even/odd class toggle code to apply the class to each table row.
• Toggle to next class when the checksum changes.
• Attach a simple css file with stock background color.

Remaining tasks

User interface changes

API changes

Data model changes