New route to delete grades

grades.go

@@ -3,6 +3,7 @@ package main
 import (
 	"log"
 	"net/http"
+	"strconv"
 
 	"github.com/gin-gonic/gin"
 )
@@ -65,6 +66,21 @@ func declareAPIAuthGradesRoutes(router *gin.RouterGroup) {
 	})
 }
 
+func gradeHandler(c *gin.Context) {
+	work := c.MustGet("work").(*Work)
+
+	if gid, err := strconv.Atoi(string(c.Param("gid"))); err != nil {
+		c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{"errmsg": "Bad grade identifier."})
+		return
+	} else if grade, err := work.GetGrade(int64(gid)); err != nil {
+		c.AbortWithStatusJSON(http.StatusNotFound, gin.H{"errmsg": "Grade not found."})
+		return
+	} else {
+		c.Set("grade", grade)
+		c.Next()
+	}
+}
+
 func GetAllGrades() (scores map[int64]map[int64]*float64, err error) {
 	if rows, errr := DBQuery("SELECT id_user, id_survey, SUM(score)/COUNT(*) FROM student_scores GROUP BY id_user, id_survey"); errr != nil {
 		return nil, errr