Ideally instead of selecting a content type for the search you would want to select a Result Source, but currently Result Sources are not
available through SharePoint's REST API.
The logic for querying the SharePoint Content Types in the properties of the webpart was in part due to Chris O'Brien and this [blog post](http://www.sharepointnutsandbolts.com/2016/09/sharepoint-framework-spfx-web-part-properties-dynamic-dropdown.html?m=0)
> Note: In order to use the ngOfficeFabric code I use the ModuleLoader to load newer source files than the currently Office Fabric UI in SharePoint Online, which will cause many of the icons not to load properly on the SharePoint Page this webpart is added to.
> Note: For the display template of the search results I'm currently using the Office Fabric UI List template. Ideally I was hoping to use the DocumentCard Component, however, that is not yet available through the ngOfficUIFabric.
> Note: The List display is not currently displaying correctly because there appears to be an issue when loading https://appsforoffice.microsoft.com/fabric/2.6.1/fabric.components.min.css which causes the dropdowns in the property pane not to work.
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