Pick your own menu bar icon, plus a tidier Settings

Settings got a proper cleanup, and you can now choose the menu bar icon
that suits you.

New

• Configurable menu bar icon. Pick from a set of icons in Settings so
  WhatCable fits in with the rest of your menu bar
  (#294).
• Redesigned Settings. The settings screen is now a native grouped
  layout that's easier to scan.

Fixes

• The self-updater no longer fails silently on standard accounts. If
  you run macOS under a non-admin account that can't write to
  /Applications, the in-app update used to fail with no message at all.
  WhatCable now spots this up front and tells you how to update instead
  (download from whatcable.uk, or use Homebrew). Thanks @renglm
  (#287).
• The Dock-app window resizes freely. In Dock-app mode (menu bar
  mode off) the window was resizable but the content stopped at a fixed
  size and clipped. It now fills whatever size you drag the window to.
  Thanks @jgates-fgsd (#281).

Other

• Tidied up the Traditional Chinese wording for consistency.