[C64] Support `.t64` format

There are multiple file types for C64 tape images; namely .tap and .t64

These file types are different, but both represent tape-stored data as opposed to disk/cartridge.

While BizHawk supports mounting both types, only the programs on .tap images can be loaded and run within the emulator.

When using .tap files, BizHawk automatically "presses" 'PLAY' on the tape drive for the user, allowing the system to load the program.

When trying to load a program from a .t64 file, the system asks the user to to "PRESS PLAY ON TAPE".
There is however no way of doing so in BizHawk (at least from what I can find), thus .t64 files are currently unusable even though they are recognized.

I suggest one of the following solutions:

1. Implement some sort of interface to be able to "PRESS PLAY" on the virtual tape drive so that t64 files can be fully loaded and run.
2. Implement the same automatic pressing of the 'PLAY' button for .t64 files that the .tap files already use.
3. Eliminate BizHawk's recognition of .t64 files if no other solution is possible to allow use of a .t64 file.