Shorten tabs with long labels.
Right now, when opening a file with a very long name, e.g. Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch.txt
the length of the tab dictates the minimum size of the window, even if this tab is not visible because of other tabs.
We need to ellpsisize the tab labels without running into issues with how the tab bar is packed.