Big code refactor

The design was defective and I didn't expect the popularity of the project. After these changes the code will be more mantainable and understandable.

Among the changes we can see:
- A better code structure
- Decoupled button widget from its logic
- More code reuse
- Easier way to add buttons
- Specialized classes

src/capture/tools/rectangletool.cpp

@@ -0,0 +1,57 @@
+// Copyright 2017 Alejandro Sirgo Rica
+//
+// This file is part of Flameshot.
+//
+//     Flameshot is free software: you can redistribute it and/or modify
+//     it under the terms of the GNU General Public License as published by
+//     the Free Software Foundation, either version 3 of the License, or
+//     (at your option) any later version.
+//
+//     Flameshot is distributed in the hope that it will be useful,
+//     but WITHOUT ANY WARRANTY; without even the implied warranty of
+//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//     GNU General Public License for more details.
+//
+//     You should have received a copy of the GNU General Public License
+//     along with Flameshot.  If not, see <http://www.gnu.org/licenses/>.
+
+#include "rectangletool.h"
+#include <QPainter>
+
+RectangleTool::RectangleTool(QObject *parent) : CaptureTool(parent) {
+
+}
+
+bool RectangleTool::isSelectable() {
+    return true;
+}
+
+QString RectangleTool::getIconName() {
+    return "square.png";
+}
+
+QString RectangleTool::getName() {
+    return tr("Rectangle");
+}
+
+QString RectangleTool::getDescription() {
+    return tr("Sets the Rectangle as the paint tool");
+}
+
+CaptureTool::ToolWorkType RectangleTool::getToolType() {
+    return TYPE_LINE_DRAWER;
+}
+
+void RectangleTool::processImage(
+        QPainter &painter,
+        const QVector<QPoint> &points,
+        const QColor &color)
+{
+    painter.setPen(QPen(color, 2));
+    painter.setBrush(QBrush(color));
+    painter.drawRect(QRect(points[0], points[1]));
+    painter.setBrush(QBrush());
+}
+
+void RectangleTool::onPressed() {
+}