Config file should be the same format as xboxdrv

[multimeric]

It seems that the ubuntu_xboxdrv config file (this one) is a custom format, that lets you specify FORCE_FEEDBACK, TRIGGER_AS_BUTTON, and MIMIC_XPAD. However, if you want to use any option other than these 3, you have to specify it as an xboxdrv flag, e.g. XBOXDRV_OPTIONS="--dpad-as-button".

I don't think it makes sense to have a custom config file, especially one that only implements a small subset of options, when xboxdrv already has a well documented config file: https://pingus.seul.org/~grumbel/xboxdrv/xboxdrv.html#idp65351024.

I think ubuntu_xboxdrv should use the original xboxdrv config file, and install it into /etc/default/xboxdrv, and then run xboxdrv with -c /etc/default/xboxdrv. This would be helpful firstly because the xboxdrv config file is much more feature complete and well-documented. Making this change would better unify the two projects, and allow people to share configs, if they're using xboxdrv or ubuntu_xboxdrv. It would also mean that people who end up on the xboxdrv manual page aren't confused as to which config format they should be using.

I'm happy to write a PR to this effect, but I'd like to check if everyone thinks this would be a reasonable change.