DiffViewer - Refactor state structure

[armenzg]

Currently we have appError, csetMeta, parsedDiff and we do data manipulations across all modules.
Instead I want to do all coverage and parsedDiff manipulations in DiffViewerContainer, plus store new data. The data structure will be like this:

{
  appError // as -is
  csetMeta // XXX: We will move information from 'coverage' into 'files'
  files: {
    filePath: {
       // The next two are to determine which files score worst and sort by it
      addedLines,
      coveredLines,
      folded, // To support folding files
    }
  }
}

[armenzg]

I'm closing this.
The original issue is handle via the caching of the main page fetching.