Fixed #listings div height

[Isaiah-Cornelius]

#listings div was too large when screen width < 800px breakpoint shifted the locations to the bottom of the screen; when scrolling to the bottom of the div, some locations would not be visible.

Now, #listings div height will not exceed the available viewable screen height.

Note: The comment on line 20 snuck through and documents my hacky code tendencies and should be destroyed. I was calling getWindowDimensions() on line 35 and getting an incorrect height value, using window.onload = getWindowDimensions instead allowed document.querySelector('#sidebarA').clientHeight to get the correct value.

Happy New Year!