[New]sort-comp: add static-variables option

[vedadeepta]

• Fixes react/sort-comp static-variables #2405
• Includes test
• Includes minor docs update

Overview of change:

Added option static-variables for checking ordering of static variables.
Default order config

 order: [
    'static-variables',
    'static-methods',
    'lifecycle',
    'everything-else',
    'render'
  ]