Default fold state should be customizable

[perdodi]

Users might be overwhelmed with the many features for first sight. Better to make fold state customizable / collapsed, where there are many, and open the first only.

E.g. in src/components/containers/PlotlyPanel.js:

const newFoldStates = new Array(numFolds).fill(this.props.collapseByDefault); // instead of merely .fill(false)