Add a Diff/Compare option to the mod conflicts tab

[metacubed]

Is your feature request related to a problem? Please describe.

If a mod's files have conflicts with another mod, users would like to easily see the differences in the two versions of the file. Currently, users have to:

1. Open one mod and go to the Conflicts tab.
2. Click "Open in Explorer" to open the folder.
3. Click "Go to..." -> other mod in the Conflicts tab.
4. Click "Open in Explorer" to open the other folder.
5. Open both files manually and compare.

Describe the solution you'd like.

On the Conflicts tab in mod details, provide a new option "Compare to...". This will show the same list as "Go to...".

When you select the mod to compare, open an external diff tool, passing both files as arguments. For example:
WinMergeU <current file> <same file from compare mod>

This will probably need a configuration page to specify the Diff tool and its argument options format.