moved slider's focusable line edit to a separate distinct reusable widget

Some of the widgets designed for Slider have uses elsewhere so now they have
been moved to allow more generic usage.

app/widget/focusablelineedit/focusablelineedit.cpp

@@ -0,0 +1,51 @@
+/***
+
+  Olive - Non-Linear Video Editor
+  Copyright (C) 2019 Olive Team
+
+  This program 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.
+
+  This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#include "focusablelineedit.h"
+
+#include <QKeyEvent>
+
+FocusableLineEdit::FocusableLineEdit(QWidget *parent) :
+  QLineEdit(parent)
+{
+
+}
+
+void FocusableLineEdit::keyPressEvent(QKeyEvent *e)
+{
+  switch (e->key()) {
+  case Qt::Key_Return:
+  case Qt::Key_Enter:
+    emit Confirmed();
+    break;
+  case Qt::Key_Escape:
+    emit Cancelled();
+    break;
+  default:
+    QLineEdit::keyPressEvent(e);
+  }
+}
+
+void FocusableLineEdit::focusOutEvent(QFocusEvent *e)
+{
+  QLineEdit::focusOutEvent(e);
+
+  emit Confirmed();
+}