feat(loadable-components): Transpile lazy and signatures configuration

[Themezv]

closes #241

This pull request brings behavior closer to babel plugin:

1. Add ability to transpile lazy from @loadable/component without hacks
2. Add ability to configure signatures. babel plugin doc

BREAKING CHANGE:

Before this changes plugin detected loadable only by loadable keyword.
After you should to configure signatures if you are using imports non from @loadable/component.
For example:

["loadable-components", { "signatures": [
    {
        "from": "myLoadableWrapper",
        "name": "default" 
    },
    {
        "from": "myLoadableWrapper",
        "name": "lazy" 
    }]
}]

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Latest commit: 4c1e65a

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