General improvements

• Moved errors to their own place.
• Improved errors output, for example for an invalid payload:

[
    {
    keyword: 'required',
    dataPath: '',
    schemaPath: '#/required',
    params: { missingProperty: 'adapters' },
    message: "should have required property 'adapters'"
    }
]

• Moved helpers to their own place.
• Updated outdated documentation (JSDoc).
• Removed external dependency (Redis).
• Fixed bug that would halt application if Redis was not set.
• Removed dependency on any ENV VAR (SCHEMA_DIR). Now a setting is available, with default values. This also frees services that import msa from declaring any ENV VAR.
• Removed any asynchronous/promise as it is no longer needed.
• ESLinted (added ;), code has been formatted.
• Fixed bug in validateEvent that was calling a schema without previously checking if the schema was there.
• Now using a Map to store schema information, better and cleaner.