Enable LMMS fullscreen and... (long title, read first line of description) (#5563)

* Enable fullscreen with hotkey & hotkey to toggle maximise in internal window

* Fix an obvious blunder

* Add fullscreen menu entry

* Change Alt+F11 to Shift+F11 (fix Windows bug)

* Move F5-F10 to Ctrl+F*, fullscreen by F11 and fix Linux bug

* Remove wrongly placed "fullscreen" attribute

* Remove temporary fixes for redundant bug

* Rename maximise to maximize

* Rename maximise to maximize

* Use fullscreen icon instead of maximise icon

* Actually include the icon in the commit

* Replace .svg icon with .png 16x16 icon

* Migrate editor hotkeys to Ctrl+1-7

include/Editor.h

@@ -62,6 +62,8 @@ private slots:
 	/// Called by pressing shift+space. Toggles pause state.
 	void togglePause();
 
+	void toggleMaximize();
+
 signals:
 
 protected:

include/MainWindow.h

@@ -155,6 +155,7 @@ public slots:
 	void toggleFxMixerWin();
 	void togglePianoRollWin();
 	void toggleControllerRack();
+	void toggleFullscreen();
 
 	void updatePlayPauseIcons();
 
@@ -224,6 +225,8 @@ private:
 	ToolButton * m_metronomeToggle;
 
 	SessionState m_session;
+	
+	bool maximized;
 
 private slots:
 	void browseHelp();