Bugfix in LabGrid class + code refactoring

- suppressed trailing `_` char for class' parameters
- renamed function name (those not related to Gtk) to lowerCamelCase
- changed the mecanism of dragging point, to avoid throwing unecessary
`panelChange` event
- added a `reset` function, with support of `toInitial` to get back the
values at load time (CTRL+click on reset button)
- `on_draw` optimisation: now LabGrid IS A BackBuffer

rtgui/labgrid.h

@@ -43,33 +43,45 @@
 #include "toolpanel.h"
 
 
-class LabGrid: public Gtk::DrawingArea {
+class LabGrid: public Gtk::DrawingArea, public BackBuffer {
 private:
-    rtengine::ProcEvent evt_;
-    enum State { OFF, HIGH, LOW };
-    State selected_;
-    float low_a_;
-    float high_a_;
-    float low_b_;
-    float high_b_;
-    ToolPanelListener *listener_;
-    bool edited_;
-    sigc::connection delay_conn_;
+    rtengine::ProcEvent evt;
+    enum State { NONE, HIGH, LOW };
+    State litPoint;
+    float low_a;
+    float high_a;
+    float low_b;
+    float high_b;
+
+    float defaultLow_a;
+    float defaultHigh_a;
+    float defaultLow_b;
+    float defaultHigh_b;
+
+    ToolPanelListener *listener;
+    bool edited;
+    bool isDragged;
+    sigc::connection delayconn;
     static const int inset = 2;
 
-    bool notify_listener();
-    
+    bool notifyListener();
+    void getLitPoint();
+
 public:
     LabGrid(rtengine::ProcEvent evt);
 
-    void get_params(double &la, double &lb, double &ha, double &hb) const;
-    void set_params(double la, double lb, double ha, double hb, bool notify);
-    void set_edited(bool yes);
-    bool get_edited() const;
-    void set_listener(ToolPanelListener *l);
+    void getParams(double &la, double &lb, double &ha, double &hb) const;
+    void setParams(double la, double lb, double ha, double hb, bool notify);
+    void setDefault (double la, double lb, double ha, double hb);
+    void setEdited(bool yes);
+    bool getEdited() const;
+    void reset(bool toInitial);
+    void setListener(ToolPanelListener *l);
 
     bool on_draw(const ::Cairo::RefPtr<Cairo::Context> &crf);
+    void on_style_updated ();
     bool on_button_press_event(GdkEventButton *event);
+    bool on_button_release_event(GdkEventButton *event);
     bool on_motion_notify_event(GdkEventMotion *event);
     Gtk::SizeRequestMode get_request_mode_vfunc() const;
     void get_preferred_width_vfunc(int &minimum_width, int &natural_width) const;