Fixed: Center icons in tables

Co-Authored-By: Mark McDowall <markus101@users.noreply.github.com>

frontend/src/Activity/History/HistoryEventTypeCell.css

@@ -1,3 +1,6 @@
 .cell {
+  composes: cell from 'Components/Table/Cells/TableRowCell.css';
+
   width: 35px;
+  text-align: center;
 }

frontend/src/Components/Page/Sidebar/PageSidebarItem.css

@@ -36,7 +36,9 @@
 
 .iconContainer {
   display: inline-block;
-  width: 25px;
+  margin-right: 7px;
+  width: 18px;
+  text-align: center;
 }
 
 .noIcon {

frontend/src/System/Backup/BackupRow.css

@@ -2,6 +2,7 @@
   composes: cell from 'Components/Table/Cells/TableRowCell.css';
 
   width: 20px;
+  text-align: center;
 }
 
 .actions {