Add Dockerfile for building firmware

[dennisdegreef]

I have added a Dockerfile so images can be build easily and contained

[mithro]

Could you move the docker stuff into its own directory?

[theshaun]

not sure of status on this (or the appropriate folder name) but some additional README to note how to use the --device flag to assist with flash the bin's onto the tomu might be useful to some

[xobs]

This patchset looks like it does two things:

1. Add a Dockerfile
2. Change the compiler to gcc-arm-none-eabi-5_4-2016q3

Please split the Dockerfile change into its own commit.