Some fixes for the new GLRenderer (#930)

* Some fixes for the new GLRenderer

Changelog:
- Fix transparency of the window on some games on Windows.
- Fix escape key not being able to exit emulation.
- Fix inverted logic in fullscreen event handling.
- Fix a race condition when stoping emulation causing a hang.
- Fix a memory leak of the OpenGL context when stoping emulation (saving ~200MB of RAM when stoping emulation).
- Simplify and document behaviours when exiting the emulator while the
emulation is running.

* Make sure to clear alpha channel when presenting Texture

This fix once and for all the transparency issue on Windows.

* Enforce footer bar size to avoid gl widget to get resized to 1280x724

* Fix full screen inversion in MainWindow and make sure _listStatusBox don't come back when not needed

* Remove previous transparency clear attempt that is useless now

* Remove an extra line return

Ryujinx/Ui/MainWindow.glade

@@ -7,7 +7,7 @@
     <property name="title" translatable="yes">Ryujinx</property>
     <property name="window_position">center</property>
     <property name="default_width">1280</property>
-    <property name="default_height">750</property>
+    <property name="default_height">760</property>
     <child type="titlebar">
       <placeholder/>
     </child>
@@ -357,7 +357,7 @@
           </packing>
         </child>
         <child>
-          <object class="GtkBox" id="MainBox">
+          <object class="GtkBox" id="_mainBox">
             <property name="visible">True</property>
             <property name="can_focus">False</property>
             <property name="orientation">vertical</property>
@@ -403,6 +403,8 @@
               <object class="GtkBox" id="_footerBox">
                 <property name="visible">True</property>
                 <property name="can_focus">False</property>
+                <property name="width_request">1280</property>
+                <property name="height_request">19</property>
                 <child>
                   <object class="GtkBox" id="_listStatusBox">
                     <property name="visible">True</property>