Multi system emulator in js

Fix scroll bar css (Thanks to @allancoding)
Flip the context menu instead of going off the page
Add hooks for save files (Thanks to @gantoine)
Add class for each virtual gamepad button
Add EJS_forceLegacyCores option
Add EJS_noAutoFocus (this is only for advanced developers, not likely an option you will use)
Added supported Amiga file extensions (Thanks to @michael-j-green)
Display the file name of the ROM/disk when using M3U lists (Thanks to @michael-j-green)
Added vsync option
Added advanced shader configuration support (Thanks to @n-at)