Allow using StringLiteral as properties of StyleSheet

[shirohana]

Try to fix #213

After Patch

Now we can lint some simple template string like: (with default configs)

const styles = StyleSheet.create({
  'Text--underlined': {},
  'Text--basic': {}
})

// `error  Expected class names to be in ascending order.
//    'Text--basic' should be before 'Text--underlined'  react-native/sort-styles`

const prefix = 'Text'
const styles = StyleSheet.create({
  [`${prefix}Wrapper`]: {},
  [`${prefix}Container`]: {}
})

// `error  Expected class names to be in ascending order.
//    'TextContainer' should be before 'TextWrapper'  react-native/sort-styles`

---

By the way, other expressions like BinaryExpression or AssignmentExpression was not implemented yet.
I think it is a little bit abusing StyleSheet?

[coveralls]

Coverage increased (+0.3%) to 75.097% when pulling 9e13485 on shirohana:fix/literal-stylesheet-property into 35f7e07 on Intellicode:master.

[coveralls]

Coverage increased (+0.3%) to 75.097% when pulling 9e13485 on shirohana:fix/literal-stylesheet-property into 35f7e07 on Intellicode:master.

[Intellicode]

@shirohana Thanks for your PR!

The initial rules were probably designed for the most simple use cases (I haven't created this rule). I suppose if there is a valid use case for BinaryExpression or AssignmentExpression it can certainly be added.