The App's <iframe> extends beyond the window

The `` that the child app lives in has its height set to `100%` which causes the "Tool Name (1)" header to push it offscreen, which is annoying when developing a plugin that normally extends beyond the vertical space. Could be fixed by using flex to fill the remaining space.

```jsx
<Grid container direction="column" item xs="auto" className={...}>
<Box m={4}>
<Grid container alignItems="center">
<Grid item xs><Typography variant="overline">Tool Name (1)</Typography></Grid>
<Grid item><IconButton onClick={this.toggleToolDrawer}>...</IconButton></Grid>
</Grid>
</Box>
<Divider />
<Grid item xs>
<iframe style={{ border: 0, height: '100%', width: '100%' }} {...} />
</Grid>
</Grid>
```