MDL-55071 theme_boost: Fix stylelint issues

Part of MDL-55071

.stylelintrc

@@ -1,11 +1,11 @@
 {
     "rules": {
         "at-rule-empty-line-before": [ "always",
-          {"except": [ "blockless-group", "first-nested" ], ignore: ["after-comment"]}
+          {"except": [ "blockless-group", "all-nested" ], ignore: ["after-comment"]}
         ],
         "at-rule-name-case": "lower",
         "at-rule-name-space-after": "always-single-line",
-        "at-rule-no-unknown": true,
+        "at-rule-no-unknown": [true, ignoreAtRules: ["extend", "include"]],
         "at-rule-semicolon-newline-after": "always",
         "block-closing-brace-newline-after": "always",
         "block-closing-brace-newline-before": "always-multi-line",

theme/bootstrapbase/less/moodle/core.less

@@ -106,7 +106,7 @@
 
 /*rtl:ignore*/
 .text-ltr {
-    direction: ltr !important;
+    direction: ltr !important;  /* stylelint-disable-line declaration-no-important */
 }
 
 #add,

theme/bootstrapbase/less/moodle/message.less

@@ -49,10 +49,8 @@ table.message .searchresults td {
 }
 .message .contactselector {
     @maxwidth: 240px;
-
     max-width: 380px;
     margin: 0 auto;
-
     @media screen and (min-width: 1000px) {
         float: left;
         padding: 0 8px 0 0;
@@ -136,7 +134,6 @@ table.message .searchresults td {
         border-left: 1px solid @tableBorder;
         padding: 0 8px;
     }
-
     @media screen and (max-width: 1000px) {
         width: 100%;
     }

theme/bootstrapbase/style/moodle.css

@@ -73,6 +73,7 @@
 /*rtl:ignore*/
 .text-ltr {
   direction: ltr !important;
+  /* stylelint-disable-line declaration-no-important */
 }
 #add,
 #remove,