Import formatting from xlsx files

We added support for importing styles from .xlsx files. When uploaded, your subset files will include, colors, borders, and cell alignments.

Other fixes

• Made the import dialog look a little nicer
• Added shortcuts for changing sheets with alt+up or down arrow
• Fixed an issue where deleting a row on a formula range another formula depended on caused an incorrect REF error
• Fixed an issue where you were unable to re-enter formula mode when between an open parenthesis and a comma