Support `import myAttr from "ember-data/attr"`

[dcyriller]

Whereas import attr from "ember-data/attr" is supported, import myAttr from "ember-data/attr" is not (yet). It will be ignored by the codemod.

updateExistingLiteralPaths function should be updated to support it.

Note that aliased named import are supported: import { hasMany as many } from "ember-data/relationships" is properly turned into import { hasMany as many } from "@ember-data/model".

Related discussion: #21 (comment)