feat: add keybinding to scroll top and bottom

[ColonelBucket8]

Feature

1. Add keybinding to scroll top and bottom
2. Change refresh keybinding to avoid conflict

#528

Checklist

• The modified code has some test-coverage (where applicable).
• make test is passing (this is what CI runs).
• New unreleased features/fixes/styling and performance improvements are documented via git: feat: / fix: / style: / perf:. Or e.g. perf(highlighting):.
  See https://github.com/altsem/gitu/blob/master/docs/dev-tooling.md