Allow actions to be passed to ItemTableAppBar

Currently, the ItemTableAppBar accepts four props: title, setDarkMode, darkMode and theme. The title and theme props work as expected. The setDarkMode and darkMode props are passed for toggling dark mode. While this works for a single action, it is not a scalable solution for more actions to be added later.

Within ItemTableAppBar, it would be relatively simple to add more actions. This is what the current dark mode toggle looks like:
```jsx
<Tooltip title={"Turn " + (props.darkMode ? "off" : "on") + " dark mode"} 
	arrow 
	onClick={toggleDarkMode} 
	TransitionComponent={Zoom}
>
	<IconButton color="inherit">
		{props.darkMode ? <DarkModeIcon /> : <LightModeIcon />}
	</IconButton>
</Tooltip>
```

This could could be made into a component with the following props:
- `tooltipTitle`: a string to show in the tooltip on hover
- `onClick`: a function to execute when the button is clicked
- `icon`: the image/vector to display when clicked

The component could be used with those components like this:
```jsx
<ItemTableAppBarAction
    tooltipTitle={"Hello World"}
    onClick={onClickHandler}
    icon={clicked ? <InactiveIcon/> : <ActiveIcon/>}
/>
```

The ItemTableAppBar could then be used without the darkMode and setDarkMode props but with the actions prop like this:
```jsx
itemViewAppBarActions = [
    <ItemTableAppBarAction
        tooltipTitle={"Turn " + (props.darkMode ? "off" : "on") + " dark mode"} 
        onClick={setDarkMode}
        icon={darkMode ? <DarkModeIcon /> : <LightModeIcon />}
    />
];

<ItemTableAppBar
    title="webqueue2"
    theme={theme}
    actions={itemViewAppBarActions}
/>
```