Better <select> components

1. Select component to make using <select> easier - same api as native control, it just adds all the markup and styles needed.
2. ChoiceSetting, an additional helper for settings modal, same as BooleanSetting. Uses Select inside but doesn't use <option>s, instead you need to pass an array with properties key, value, label, like BooleanSetting it also completely handles defaults (modified indicator + '(default)' in options) by itself.
3. Some minor refactorings like selects in poll form now use .unstyled instead of resettting styles.