batches: resize SSBC editor to remaining screen height

Created by: courier-new

Soooooooo let's just ignore the fact that I first implemented this completely by hand with DOM element sizes and window resize listeners because I thought the underlying editor component only accepted a height in pixels. 😅 Turns out we just only accepted a height in pixels and I'm bad at assumptions.

This just adapts our implementation of the editor component to accept strings so that we can set the SSBC editor height to a percentage like '100%'. The behavior for numbers and 'auto' is retained.