Table improvements

Part 3 in our recurring series of improvements to tables in Outline. This release includes the following updates: Table columns and rows can now be reordered by dragging the column or row header to a new position Table cells can now have a custom colored background, use the new “Cell background” option in the toolbar to choose a color Sorting of table data is more natural for currencies, dates, and numbers Lists inside tables no longer break Markdown output Tables with merged cells now behave correctly when sorting Other improvements Added the ability to choose custom color highlights for text