Remove requirement for an interactive shell when installing through LuCI

[muelli]

Currently, we have a preinst script which asks for confirmation if the version is not known to be compatible.

When installing through LuCI, we cannot receive terminal input.

I suggest the interactive dialogue to be removed. Or at least gated to determine whether we have stdin on a tty (e.g. if [ -t 0 ]).

We currently require "gl-sdk4-mcu" for installation of the package which suggests that the "sdk4" series is requires, which I assume is expressing the compatibility well enough. If we learn about incompatible firmware versions, we can probably depend on a specific version of gl-base-files. We should further include gl-base-files-e750 to limit installation on E750 devices.

We could render suspected incompatibilities on the Blue-Merle Web interface.

[nestire]

I actually like that there is this, since it insures that we test against new firmware releases regularly. I Understand that this creates some maintenance but this seems to be ok to me(bump the version check if the install + functions are working which takes around 1 Hour to check). There seems to be a new Firmware release every 2-3 Month I would say this is fine.