* Rework repo buttons

- Replace "New PR" and "Go to File" button with Icon Button
- Move all "Add File" actions into a dropdown button
- Remove most custom styling of clone buttons
- Margin and wiki tweaks

Buttons are now all equal height, mobile layout wraps gracefully.

Fixes: go-gitea#13671
Replaces: go-gitea#20375

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

…ea#20718)

Fix two regressions from go-gitea#20602:

- Restore the 'History' button that was previously unable to render
  because it's show condition was never hit
- Hide the 'Add File' button when there would be no items in the
  dropdown.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>