Disable hardware decoding when using blur_edges

[Nudin]

Hardware decoding will most often interfer with the filter, therefore disable
it when enabling of blur_edges and restore the original value when disabling.

If you think it would be better to implement this feature as an opt-in/opt-out
feature let me know.

[occivink]

I think it would make sense to make this behavior configurable, and simply just warn and abort by default.
If I remember correctly, filters can also be used with all the *-copy hardware decoders.

[Nudin]

If I remember correctly, filters can also be used with all the *-copy hardware decoders.

At least on my system it also doesn't work with the -copy versions.

I made it configurable and documented it in the config file. I mad it enable by default, since if it is set to false the script will likely not work for several users, without any benefit.

[shibotto]

This would be very nice to have for crop.lua as well.