title: Override Material UI shadow array values in theme overrides using createMuiTheme
body: <p>I have a custom theme for my toolkit and am using <code>createMuiTheme</code> to override the palette, fonts, etc. I am attempting to slim down the <code>shadow</code> array in the theme object which is used for various components, which by default comes with 25 values. I only want to offer two options in my shadow array to keep things simple.</p>
  
  <p>When I pass the two values I want to support for shadows into the array I get a warning from MUI: </p>
  
  <pre><code>index.js:1437 Warning: Material-UI: the shadows array provided to createMuiTheme should support 25 elevations.
  </code></pre>
  
  <p>So i've gotten around this by adding setting "none" for the other shadows that I don't want set values for like so: </p>
  
  <pre><code>let theme = createMuiTheme({
    palette: {
      common: {
        black: "#000",
        white: "#fff",
        ...
      },
    typography: {
      fontFamily: opensans,
      ...
    },
    shadows: [
      `0px 0px 6px 0px ${hexa(grey[500], 0.25)}`,
      `0px 0px 6px 0px ${hexa(grey[500], 0.55)}`,
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
      "none",
     etc...
    ]
  });
  </code></pre>
  
  <p>This is not ideal since it bloats the theme a ton which developers use as a ref to see whats available to use, is there a way around this?  </p>
  
  <p>My ideal state is representation in the theme object that looks like this but with no console warnings:</p>
  
  <pre><code>let theme = createMuiTheme({
    palette: {
      common: {
        black: "#000",
        white: "#fff",
        ...
      },
    typography: {
      fontFamily: opensans,
      ...
    },
    shadows: [
      `0px 0px 6px 0px ${hexa(grey[500], 0.25)}`,
      `0px 0px 6px 0px ${hexa(grey[500], 0.55)}`,
    ]
  });
  </code></pre>