Web 46: Add split component

[gracesilge]

• Creates composable split component
• Allows for any realistic ratio
• In a vertical behavior or small screen size, the component will act like 2 content blocks stacked on top of each other, allowing components to determine their own size

Open questions/future improvements:

• If one content block is significantly larger than another, the smaller content defaults to the top, creating a big gap (see first image). Should we find a way to make it default to the middle, or is this unimportant because you would simply decrease the ratio in the case of a big difference in size?
• Should we make a horizontal-only split pane - one that does not default to vertical on mobile? I used a split pane to make the button smaller in the example, but that behavior was lost on mobile.

Horizontal and big screen:

Small screen:

Vertical selection: