Organise boards selector: spacer between board families

[jrial]

This PR was not requested; feel free to suggest improvements, or to decline if you disagree with my changes. It was created because I always have trouble finding the right board in the long, flat and unsorted boards list. While I haven't implemented sorting (new to Coffeescript), I did add the following improvements which I find help me locate my boards quicker in the board selection:

• Adds board family name, uppercased, between the different board families (Arduino, ESP32, ESP8266)
• Adds a spacer between different board families to aid in locating the correct section
• Renames '== Arduino Setting ==' to more descriptive 'Use Arduino IDE Setting'
• Removes the redundant '== Custom Setting ==' entry.

Screenshots:

[StaticRocket]

A nice idea, however I believe editing the menu's style could achieve a similar effect without allowing the user to select a null board.