Ivan - Fix modal positioning [skip ci]

client/src/app/app.scss

@@ -2,11 +2,4 @@
 
 .application {
     padding: $half-space;
-
-    &_modal-opened {
-        .application__content {
-            position: fixed;
-            overflow: hidden;
-        }
-    }
 }

client/src/core-components/modal.scss

@@ -1,11 +1,14 @@
 .modal {
-    position: absolute;
+    position: fixed;
     top: 0;
     left: 0;
     background-color: rgba(0, 0, 0, 0.8);
     width: 100%;
     height: 100%;
     display: flex;
+    padding: 50px 0;
+    overflow: auto;
+    z-index: 1000;
 
     &__content {
         position: relative;

client/src/reducers/modal-reducer.js

@@ -19,6 +19,8 @@ class ModalReducer extends Reducer {
     }
 
     onOpenModal(state, payload) {
+        document.body.setAttribute('style', 'overflow:hidden');
+
         return _.extend({}, state, {
             opened: true,
             content: payload
@@ -26,6 +28,8 @@ class ModalReducer extends Reducer {
     }
 
     onCloseModal(state) {
+        document.body.setAttribute('style', '');
+        
         return _.extend({}, state, {
             opened: false,
             content: null