Add Text tool

closes #11
Add an initial version of the text tool.
This commit adds:
- Basic text tool.
- On demand thickness and color update.
- Generalized logic for future widget based tools.

src/tools/abstractactiontool.cpp

@@ -69,3 +69,11 @@ void AbstractActionTool::drawMove(const QPoint &p) {
 void AbstractActionTool::drawStart(const CaptureContext &context) {
     Q_UNUSED(context);
 }
+
+void AbstractActionTool::colorChanged(const QColor &c) {
+    Q_UNUSED(c);
+}
+
+void AbstractActionTool::thicknessChanged(const int th) {
+    Q_UNUSED(th);
+}