Add configurable options to optimise CSS

[pancaspe87]

Is your feature request related to a problem? Please describe. At current Compiled applies additional plugins) to optimise CSS based on the value of process.env.NODE_ENV . However, if the variable is undefined in one of the environment this could cause a mismatch between server and browser if they have different configuration when stylesheet extraction is enabled.

For example, given margin-top: 32px; this will become margin-top: 2pc; in production mode. Because of these different CSS values, Compiled will generate different CSS classes and cause browser/server not to be on sync