Added fieldsArea class to add fields to primaryFields, secondaryFields, etc

fields.js

@@ -0,0 +1,39 @@
+const schema = require("./schema");
+
+class FieldsArea {
+	constructor() {
+		this.fields = [];
+	}
+
+	push(...fields) {
+		if (fields[0] instanceof Array && fields[0].length) {
+			fields = fields[0];
+		}
+
+		let validFields = fields.filter(f => typeof f === "object" && schema.isValid(f, schema.constants.field));
+
+		this.fields.push(...validFields);
+
+		return validFields.length;
+	}
+
+	pop(quantity = -1) {
+		if (!this.fields.length) {
+			return undefined;
+		}
+
+		if (quantity > -1) {
+			let removedElements = this.fields.slice(quantity);
+			this.fields = this.fields.slice(0, this.fields.length - quantity);
+
+			return removedElements;
+		}
+
+		return this.fields.pop();
+	}
+}
+
+module.exports = {
+	areas: ["primaryFields", "secondaryFields", "auxiliaryFields", "backFields", "headerFields"],
+	FieldsArea
+};