feat(react-modifier) Allow children prop to be passed

[jvidalv]

Description

Right now, passing children to the component does not work, the only children allowed was the one passed within ember while leveraging yield and block features.

This MR allows to pass a direct children prop from the ReactBridge component which will take preference over the block one.

  <ReactBridge
          @reactComponent={{this.reactExample}}
          @props={{hash children="Works string"}}
        />

It does also allow to pass ReactNodes:

 <ReactBridge
         @reactComponent={{this.reactExample}}
         @props={{hash children=this.reactExample}}
       />