Merge branch 'extend_headers_to_meta' into 'master'

Extend headers to meta

This MR includes the Enc and Sig pseudoheaders in the list of configurable headers. This makes it possible to rearrange or disable them.
Fixes #297

See merge request schleuder/schleuder!147
Status Job ID Name Coverage
  Static
canceled #69614
allowed to fail
changelog

canceled #69615
codespell

 
  Test
canceled #69616
ruby:2.1

canceled #69617
ruby:2.2

canceled #69618
ruby:2.3

canceled #69619
ruby:2.4

canceled #69620
ruby:2.5

 
  Debian:Build
canceled #69621
allowed to fail
debian:build

 
  Debian:Qa
canceled #69622
allowed to fail
debian:autopkgtest

canceled #69623
allowed to fail
debian:lintian