Add custom refresh rate mode to VSync option (#238)

Rebased @jcm93's refreshinterval branch:
https://github.com/jcm93/Ryujinx/tree/refreshinterval

The option is placed under System/Hacks. Disabled, it's the default
Ryujinx behavior. Enabled, the behavior is shown in the attached
screenshots. If a framerate is too high or low, you can adjust the value
where you normally toggle VSync on and off. It will also cycle through
the default on/off toggles.

Also, in order to reduce clutter, I made an adjustment to remove the
target FPS and only show the percentage.

---------

Co-authored-by: jcm <6864788+jcm93@users.noreply.github.com>

src/Ryujinx/Assets/Styles/Themes.xaml

@@ -26,8 +26,9 @@
             <Color x:Key="AppListBackgroundColor">#b3ffffff</Color>
             <Color x:Key="AppListHoverBackgroundColor">#80cccccc</Color>
             <Color x:Key="SecondaryTextColor">#A0000000</Color>
-            <Color x:Key="VsyncEnabled">#FF2EEAC9</Color>
-            <Color x:Key="VsyncDisabled">#FFFF4554</Color>
+            <Color x:Key="Switch">#FF2EEAC9</Color>
+            <Color x:Key="Unbounded">#FFFF4554</Color>
+            <Color x:Key="Custom">#6483F5</Color>
         </ResourceDictionary>
         <ResourceDictionary x:Key="Light">
             <SolidColorBrush x:Key="DataGridSelectionBackgroundBrush"