[IMP] web_calendar: fine tuning less

Use webclient horizontal padding in calendar view for its content
to be well aligned with the rest of the webclient.

addons/web_calendar/static/src/less/web_calendar.less

@@ -1,6 +1,8 @@
+@o-calendar-div-padding: 4px;
+@nb-calendar-colors: 24;
 
 .o_calendar_container {
-    @nb-calendar-colors: 24;
+    padding: @o-calendar-div-padding (@odoo-horizontal-padding - @o-calendar-div-padding);
 
     .calendar_color_loop(@index) when (@index < @nb-calendar-colors+1) {
         .o_calendar_color_@{index} {
@@ -22,7 +24,7 @@
     .underline_color_loop(1);
 
     .o_calendar_view {
-        padding: 8px;
+        padding: @o-calendar-div-padding;
 
         .o_calendar_widget {
             background-color: @odoo-view-background-color;
@@ -42,8 +44,7 @@
     }
 
     .o_calendar_sidebar_container {
-        padding: 8px;
-        padding-left: 0;
+        padding: @o-calendar-div-padding;
 
         .ui-datepicker {
             width: 100%;