Cosmetic: Declare a GUID constant for Morgan's Stream Switcher.
Cosmetics: Try to use CLSID constants when available.
Subtitle input pin: remove a useless lock.
Prevent black lines from appearing on the sides of the video when resizing.

This happened mostly when resizing manually or when using auto-fit zoom.

Fixes #2423.
ISR: Show all subtitles tracks in the Play > Subtitles menu.

All subtitles tracks available will be shown in the Play > Subtitles menu when using the internal subtitles renderer. That includes all the embedded tracks exhibited by the source filter and the external tracks.
"Play > Subtitles" menu: simplify the items' state handling.

This menu is dynamically build so there is no reason to use an extra function to set the state of its items. The states are now set correctly when building the menu.

Note that thanks to this change the new UI style is now used for the radio bullet.
Cosmetic: remove useless flags from CMenu::AppendMenu calls.
"Play > Audio" menu: simplify the items' state handling.

This menu is dynamically build so there is no reason to use an extra function to set the state of its items. The states are now set correctly when building the menu.

Note that thanks to this change the new UI style is now used for the radio bullet.
Cosmetics.