add support to --merge jsons for pvr fastcopy command

See merge request !367

set build-tags artifacts to never expire

See merge request !364

remove root.squashfs.new file before running mksquashfs

See merge request !362

fix whiteout removal if symlinks are dead by using os.Lstat; add debugging output

See merge request !361

fix destfragement behaviour on fastcopy

See merge request !360

Resolve "pvr fail with no warning if squashfs-tools are not installed"

Closes #13

See merge request !359

feat(sign): download certificates from gitlab if .pvr/pvs folder is empty

See merge request !358

support putting default keys and certs in ~/.pvr/pvs

See merge request !357

We support:
 - key.default.pem (secret key)
 - x5c.default.pem (default x5c certchain)
 - cacerts.default.pem (default trusted root certs)

add support for "drivers" element in platform run.json.

See merge request !356

- .Source.args.PV_DRIVERS_MANUAL - manual drivers
- .Source.args.PV_DRIVERS_REQUIRED - required drivers
- .Source.args.PV_DRIVERS_OPTIONAL - optional drivers

Feature/yocto build

See merge request !355

template[builtin-lxc-docker.go]: add support for providing custom...

See merge request !354

template[builtin-lxc-docker.go]: add support for providing custom lxc.namespace.keep config through .Source.args.PV_LXC_NAMESPACE_KEEP

drop a OK printf that caused a 'dirty' CLI output experience on clone

See merge request !353

Feature/removal on deploy

See merge request !351

Merge back 'master' into 'develop' after 031 release

See merge request !350

Merge Develop into Master for 031

See merge request !349

add support for PV_GROUP in docker templates to define 'group' element in run.json

See merge request !348

add support for PV_CONDITIONS in pvr docker template

See merge request !347

fix 'data' containers lack persistence/volume info in generated run.json

See merge request !346