title: Add custom add-button in material-table
body: <p>Currently I have a simple material-table like this:</p>
  <pre><code>&lt;MaterialTable
      options={myOptions}
      title=&quot;MyTitle&quot;
      columns={state.columns}
      data={state.data}
      tableRef={tableRef} // Not working
      editable={{
        onRowAdd: ...,
        onRowDelete: ...,
        onRowUpdate: ...
      }}
    /&gt;;
  </code></pre>
  <p>where I'm trying to a create new add button (not edit the current one): each Row in the Bar Column should have a custom add button. I've looked through the MaterialTable source code but I couldn't reproduce the code that is used for the default add button which is:</p>
  <pre><code>        calculatedProps.actions.push({
            icon: calculatedProps.icons.Add,
            tooltip: localization.addTooltip,
            position: &quot;toolbar&quot;,
            disabled: !!this.dataManager.lastEditingRow,
            onClick: () =&gt; {
              this.dataManager.changeRowEditing();
              this.setState({
                ...this.dataManager.getRenderState(),
                showAddRow: !this.state.showAddRow,
              });
            },
          });
  </code></pre>
  <p>in particular I can't get to access the <code>dataManager</code> variable.</p>
  <p><a href="https://i.stack.imgur.com/9wEzH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9wEzH.png" alt="current table" /></a></p>
  <p>That is how the current table looks like, and I need to add the add button where there is the red sign.</p>