dynamic maximum size of GCodeBuffer

[woutgg]

Currently, the GCodeBuffer has a hard-coded maximum size of 3MiB. It might be useful if it could lower this maximum dynamically based on the amount of free memory. Perhaps sysinfo could come in handy.

[woutgg]

Another reason why this can be useful is in circumstances where more memory is available, it could allow for more data to be stored or even disable the limit.

This might be useful when using the server on larger machines, especially when sending files using the front-end which are larger than the limit, which is currently impossible.

Another case where this can be useful is when external storage is attached to the wifibox, which for instance allows for a swap partition.