x, y and z error bars should have different attributes #621

At the moment, all error bar containers (i.e. error_x, error_y and error_z) are linked to the same attribute declarations found in src/components/errorbars/attributes.js.

But, the error bar attributes contains container-specific attributes, namely, copy_ystyle and copy_zstyle (see here). These attribute should only be shown in the relevant containers.

The solution would be make the src/components/errorbars/attributes.js export a function that return attributes specific to the container e.g.:

// in traces/scatter/attributes.js

var errorBarAttributes = require('../../components/errorbars/attributes');

module.exports = {
  // ...

  error_x: errorBarAttributes('x'),
  error_y: errorBarAttributes('y')
};

similar to what PR #609 put forward for colorscale attributes.