[FIX] web: scroll view in community

Since the merge of the two modules 'web' from enterprise and community
it was impossible to scroll in the side menu and in the main content
of a community database from Internet Explorer 10 & 11 but it is working in
Edge.

This was due to missing css 'height' attribute on the '.o_main' class
that should be set to 100% for IE to let the flex elements know the
size of their parent.

This was introduced in rev https://github.com/odoo/odoo/commit/977db823c

addons/web/static/src/less/webclient_layout.less

@@ -34,6 +34,7 @@
         .o-flex(1, 1, auto);
         .o-flex-display();
         min-height: 0; // Allow flex to shrink this element as much as it wants
+        height: 100%;
 
         .o_sub_menu {
             .o-flex(0, 0, @odoo-submenu-width);