Custom `<select>` element implementation (`DropdownField`)

[andersevenrud]

Sine the standard <select> DOM element has browser specific behavior and styling, it would be better to have a custom implementation.

• Use <input type="text" /> as base
• Dropdown with options
• Keybindings for navigating options
• Blur event to make dropdown disappear when no longer focused

[hello-smile6]

Yay!