AUI-1671 Convert scheduler 'view' buttons into a dropdown list

Hi @brandizzi, @juanferrub, @jonmak08,

Here is an update for https://issues.liferay.com/browse/AUI-1671.

I converted the button group for scheduler views into a dropdown list using the select element (see ticket for images). This dropdown list is not responsive and will be visible at all times on different viewport sizes. I didn't create a responsive dropdown menu for the buttons because I want to keep the code simple. If we want the buttons to collapse into a dropdown menu on mobile, we'll need to create a separate dropdown menu, show it on mobile and hide the buttons. This will add a lot of code to the src since there's no easy way of implementing a responsive navbar in aui. We also need to add a lot of custom styling to the navbar to make it look like the one you requested. Let me know if this alternative works. If not, I can change it.

Note: This pull is not complete yet. I still need to update the dropdown's ARIA attributes and unit test if we decide that we want to use this change.