Add limits endpoints

In this merge request, the following is changed:

• The API is updated to have endpoint for limits
• The endpoints for retrieving and updating the user set limits in the database are put in place.

src/main/java/nl/tudelft/ewi/tam/beans/Limits.java

+package nl.tudelft.ewi.tam.beans;
+
+/**
+ * This class embodies the Limits table of the database.
+ */
+public class Limits {
+
+    /**
+     * The ints representing the period on which the limits apply.
+     */
+    private int year,
+            quarter;
+
+    /**
+     * The ints representing the limits of the hour and courses.
+     */
+    private int hourLimit,
+            courseLimit;
+
+    /**
+     * Instantiate a new Limits instance using the provided initial variable values.
+     *
+     * @param year          the year where the limits apply
+     * @param quarter       the quarter where the limits apply
+     * @param hourLimit     the limit on the hours
+     * @param courseLimit   the limit on the courses
+     */
+    public Limits(final int year, final int quarter, final int hourLimit, final int courseLimit) {
+        this.year = year;
+        this.quarter = quarter;
+        this.hourLimit = hourLimit;
+        this.courseLimit = courseLimit;
+    }
+
+    /**
+     * Instantiate a new Limits instance without instantiated variables.
+     */
+    public Limits() {
+        // Intentionally left empty. This constructor is used for serializing json objects by the jackson library.
+    }
+
+    /**
+     * Sets new courseLimit.
+     *
+     * @param courseLimit new value of courseLimit
+     */
+    public void setCourseLimit(final int courseLimit) {
+        this.courseLimit = courseLimit;
+    }
+
+    /**
+     * Gets year.
+     *
+     * @return value of year
+     */
+    public int getYear() {
+        return year;
+    }
+
+    /**
+     * Gets quarter.
+     *
+     * @return value of quarter
+     */
+    public int getQuarter() {
+        return quarter;
+    }
+
+    /**
+     * Gets courseLimit.
+     *
+     * @return value of courseLimit
+     */
+    public int getCourseLimit() {
+        return courseLimit;
+    }
+
+    /**
+     * Gets hourLimit.
+     *
+     * @return value of hourLimit
+     */
+    public int getHourLimit() {
+        return hourLimit;
+    }
+
+    /**
+     * Sets new hourLimit.
+     *
+     * @param hourLimit new value of hourLimit
+     */
+    public void setHourLimit(final int hourLimit) {
+        this.hourLimit = hourLimit;
+    }
+
+    /**
+     * Sets new year.
+     *
+     * @param year new value of year
+     */
+    public void setYear(final int year) {
+        this.year = year;
+    }
+
+    /**
+     * Sets new quarter.
+     *
+     * @param quarter new value of quarter
+     */
+    public void setQuarter(final int quarter) {
+        this.quarter = quarter;
+    }
+}