Update dpkgfiles to support building raspberry pi armhf .deb

[phoenix-xbt]

Requires new build dependency "hardening-wrapper" when making armhf debian package with RPi toolchain.
If I have time I'll see if I can get it to play nice with different build option variables and without hardening-wrapper. Normal builds should run fine without it at least.
hardening-wrapper is gone! ✔️
Tested with debhelper v9 compat rules in effect. It'd be nice to set that but would in theory need to increase the debhelper dependency version to match.

My python is pretty scrappy at best but improvements welcomed all over.

Normal use of dpkgfiles/make_deb_package.py is retained as is.
Raspberry Pi builds are enabled by running

dpkgfiles/make_deb_package.py --cross=armhf \ 
--toolchain-path=/home/armory/RPi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin \
--extra-python-includes=/home/armory/RPi/usr/include

(Short flags available)
Substitute paths for toolchain and the extrapython path for real ones. Validates enough to know if a directory exists but it is not smart enough to know if the directory actually contains the files needed.

I have yet to test the packaged deb files on real hardware, but compiles completed fine to the best of my knowledge.

[phoenix-xbt]

Improved implementation and I've tested on a Pi with Raspbian Stretch now. Managed to create a new offline wallet without any problems.

[phoenix-xbt]

Hi @goatpig, I know you and @droark are busy with 0.97 but is there anything I need to fix or change in this PR?
Created in response to https://bitcointalk.org/index.php?topic=5135648

[goatpig]

This PR is fine as is. I'll get back to you if I need help merging this into the 0.97 build system. Thanks.

[phoenix-xbt]

Good to know, thanks.
Just to note: if the CMake build tools PR #590 gets merged this PR (and make_deb_package.py) may be largely redundant/obsolete. When I was researching possible solutions I came across CMake frequently.
It has been a while now but I think the gist was that you needed a cross compile target for CMake and then a few lines so that CPack would package it up as a .deb. All at least sounded rather painless compared to wrangling with dpkg and debhelper.