Rename PAINT to PALETTE

[joepetrowski]

PAINT (formerly the SRML) becomes PALETTE. Modules inside of Palette are called Pallets. Pallets can be combined to assemble your runtime.

How to think of pallets, by Gav:

A pallet is a standardised "shipping container" (doesn't actually house anything so much as acts as a support structure) which may host arbitrary goods. Many different pallets are typically combined to create a "final" product. The same kind of pallet-based shipment may be (re)used for multiple consumers/end products. Pallet, as a pluralistic standardised host which forms the basis for domain-specific cargo, is used as the general name for crates/modules that contain a domain-specific SRML module.

The following modules remain palette- prefixed as they do not contain domain-specific logic. Rather, they support Palette interfaces.

• Executive
• Metadata
• Support
• System
• Utility

See docs/Structure.adoc for more info.

[gnunicorn]

Minor suggestions.

[joepetrowski]

Polkadot PR: paritytech/polkadot#600