Improve responsiveness on tiny screens

[fedarko]

• Autoselection inputs are hard to read
• Search boxes in the DataTables extend past the bottom left div's right border
• The bar width controls look kind of gross (this is likely due to the hacky spacer inputs messing things up)

See screenshot for reference (edit from like 9 months later: wait what screenshot?? sheesh). None of these problems are showstoppers, esp. since we mostly advise using this on a computer, but it'd be nice to address these (along with #121) so that we can more confidently say that Qurro is usable/works well on a phone.