feat: make remBase configurable

RockFrontend.module.php

@@ -171,7 +171,8 @@ public function init()
     $this->alfredCache = $this->wire(new WireData());
 
     // JS defaults
-    $this->remBase = 16; // default base for px-->rem conversion
+    // set the remBase either from config setting or use 16 as fallback
+    $this->remBase = $this->remBase ?: 16;
     $this->initPostCSS();
 
     // watch this file and run "migrate" on change or refresh
@@ -2520,6 +2521,13 @@ private function configSettings($inputfields)
     $f->notes = $this->showFontFileSize();
     $fs->add($f);
 
+    $f = new InputfieldInteger();
+    $f->name = 'remBase';
+    $f->label = 'REM base font size';
+    $f->value = $this->remBase;
+    $f->notes = 'See [this forum thread for more info](https://processwire.com/talk/topic/29268-fr-make-rembase-a-config-setting/)';
+    $fs->add($f);
+
     $f = $this->wire->modules->get('InputfieldCheckboxes');
     $f->name = 'features';
     $f->label = "Features";