[N09] Naming issues

[cylon56]

To favor explicitness and readability, several parts of the contracts may benefit from better naming. Here are some examples:

• The name CometProxyAdmin suggests that it is only the admin of the Comet proxy, but in reality, it will also have the same role on the Configurator proxy. Choose another name to avoid confusion.
• TransparentUpgradeableConfiguratorProxy can be called ConfiguratorProxy. There is no need to use the inherited contract name as a prefix.
• In CometMath, change InvalidUInt to InvalidUint and toUInt to toUint.
• rescale and descale have different names but the same value, consider using one variable name scale.

[jflatow]

There are some good points made about the chosen names, however naming is a notoriously hard problem and we believe it is difficult if not impossible to make everyone happy. We adopted some of the proposed changes in #433.