Add header to materials collection React component

[pjanik]

Adds optional header to materials collection component. It will be rendered only if the number of materials in collection is > 0.

@emcelroy, you would need to modify calls to renderMaterialsCollection:

 Portal.renderMaterialsCollection(13, '#collection-1', {limit: 10, header: 'Why do fishermen need forests?'}); 

and remove static headers defined in HTML. Header will be rendered as H1 element with class collection-header, so it can be additionally styled on the home page.

[scytacki]

@pjanik will you be able to add the callback to this today or tomorrow?

[pjanik]

@scytacki, sorry, I forgot about it. Yes, I can do it for sure.

[pjanik]

Done, example:

 Portal.renderMaterialsCollection(13, '#collection-1', {
  limit: 10, 
  onDataLoad: function (materials) {
    console.log('downloaded ' + materials.length + ' materials');
  },
  header: 'Test header'
}); 

[scytacki]

👍