Better PR sidebar, tab loading indicators and redraw builtin

• The PR sidebar saw some improvements
  • the PR summary is now limited to 500 characters with an ability to expand it (e by default)
  • the number of files changed / additions / deletions and number of commits is now shown in the overview tab
  • some fixes to the checks and files tab
• If you have drawing issues, you can now bind the redraw builtin command
• Tabs will now show a loading indicator

Changelog

• cd22afc Fix glamour link in README.md
• d16610d Fix go.sum
• ed35728 chore: bump bubbles v0.18.0 => v0.21.0
• 556cd98 feat: add redraw builtin key-binding, unbound
• eb2624d feat: changes summary
• 7bb2f79 feat: merge as admin
• 33b51f7 feat: set proper inputbox limit (pr/issue)
• 403a213 feat: show loading indicator in tab name
• 83d59e0 feat: summary view more
• f2fbad5 fix(pr-sidebar): allow long file names
• c06efe8 fix: empty checks + sidebar fixes