FolderPicker: fix to get folders of other site.

Fix folderpicker to get folders of other site instead of the current context by adding a new property siteAbsoluteUrl and forwarding it to FolderExplorer.
Fix pnp#1305

Author: NishkalankBezawada

src/controls/folderPicker/FolderPicker.tsx

@@ -87,6 +87,7 @@ export class FolderPicker extends React.Component<IFolderPickerProps, IFolderPic
               defaultFolder={this.state.selectedFolder}
               onSelect={this._onFolderSelect}
               canCreateFolders={this.props.canCreateFolders}
+              siteAbsoluteUrl={this.props.siteAbsoluteUrl}
             />
           </div>
         </Panel>

src/controls/folderPicker/IFolderPickerProps.ts

@@ -7,6 +7,11 @@ export interface IFolderPickerProps {
    */
   context: BaseComponentContext;
 
+  /**
+   * The absolute url of the target site. Only required if not the current site
+   */
+  siteAbsoluteUrl?: string;
+
   /**
    * The label for the control
    */