added predefined mime types list and other minor ui improvements

ui/src/scss/_form.scss

@@ -800,7 +800,7 @@ select {
     outline: 0;
     .option {
         user-select: none;
-        column-gap: 8px;
+        column-gap: 5px;
         .icon {
             min-width: 20px;
             text-align: center;
@@ -910,9 +910,9 @@ select {
             max-width: 100%;
             line-height: normal;
         }
-        &:hover {
-            cursor: pointer;
-        }
+    }
+    &:not(.disabled) .selected-container:hover {
+        cursor: pointer;
     }
     &.disabled {
         color: var(--txtDisabledColor);
@@ -978,7 +978,7 @@ select {
         }
         .options-list {
             overflow: auto;
-            max-height: 270px;
+            max-height: 240px;
             width: auto;
             margin-left: 0;
             margin-right: -5px;