Reorganise configuration

[bcaudan]

configuration is a bit messy, it could be clearer with something like:

{
  suite: {
    displayNumber: false,        // display each suite number (hierarchical)
  },
  spec: {
    displayStacktrace: false,   // display stacktrace for each failed assertion
    displaySuccessful: true,    // display each successful spec
    displayFailed: true,            // display each failed spec
    displayPending: false,       // display each pending spec
    displayDuration: false,      // display each spec duration
  },
  summary: {
    displayStacktrace: false,   // display stacktrace for each failed assertion
    displaySuccesses: false,  // display summary of all successes after execution
    displayFailures: true,        // display summary of all failures after execution
    displayPending: true,       // display summary of all pending specs after execution
  },
  colors: {
    success: 'green',
    failure: 'red',
    pending: 'yellow'
  },
  prefixes: {
    success: '✓ ',
    failure: '✗ ',
    pending: '* '
  },
  customProcessors: []
}

It should still work with the previous configuration version to avoid to break all the existing integration.
Custom processors using default options would probably need to be rewrited.