Trigger requestDraw when changing TextElement text (#89)

* Fix #85 - orx-panel requestDraw() call

* Clean up imports

orx-panel/src/demo/kotlin/DemoHorizontalLayout01.kt

@@ -7,7 +7,6 @@ import org.openrndr.panel.controlManager
 import org.openrndr.panel.elements.button
 import org.openrndr.panel.elements.div
 import org.openrndr.panel.elements.h1
-import org.openrndr.panel.elements.requestRedraw
 import org.openrndr.panel.style.*
 
 fun main() = application {
@@ -66,7 +65,6 @@ fun main() = application {
                                     // the header text with the button's label
                                     events.clicked.listen {
                                         header.replaceText(it.source.label)
-                                header.requestRedraw()
                                     }
                                 }
                             }

orx-panel/src/main/kotlin/org/openrndr/panel/elements/TextElements.kt

@@ -70,12 +70,14 @@ class P : TextElement(ElementType("p"))
 abstract class TextElement(et: ElementType) : Element(et) {
     fun text(text: String) {
         append(TextNode(text))
+        requestRedraw()
     }
     fun replaceText(text : String) {
         if (children.isEmpty()) {
             text(text)
         } else {
             (children.first() as? TextNode)?.text = text
+            requestRedraw()
         }
     }
 }