add container support

src/jsMain/kotlin/dev/inmo/jsuikit/modifiers/UIKitContainer.kt

@@ -0,0 +1,19 @@
+package dev.inmo.jsuikit.modifiers
+
+sealed class UIKitContainer(
+    override val classes: Array<String> = emptyArray(),
+    override val otherAttrs: Map<String, String> = emptyMap()
+) : UIKitModifier {
+
+    sealed class Size(size: String) : UIKitContainer(arrayOf("uk-container-$size")) {
+        object XSmall : Size("xsmall")
+        object Small : Size("small")
+        object Large : Size("large")
+        object XLarge : Size("xlarge")
+        object Expand : Size("expand")
+    }
+
+    companion object : UIKitContainer(
+        arrayOf("uk-container")
+    )
+}