Add snapshot testing for react components

[kryptokinght]

• Use Jest and Enzyme setup to add boilerplate setup for snapshot testing of react components.
• Also update the README and CODETOUR.md with documentation about the snapshot testing and the folder structure required for the testing - something on the lines of https://github.com/GirlScriptSummerOfCode/Upay/blob/master/CODETOUR.md#testing