Will fix `check that rsvg-convert is in path` error when including a figure in .svg format in one of the markdown files

pandoc changed from --filter=pandoc-citeproc to --citeproc ...

* pdf is double sided
* new chapters start always on a fresh (right) page
* thus chapters may and with a blank left page

should fix #7

somehow the current chapter and section is not used in page headings if the
chapter/section is unnumbered. redefining leftmark and rightmark using markboth
seems to fix this.

see also https://www.gnu.org/software/make/manual/make.html#index-CURDIR
and https://stackoverflow.com/questions/3050231/how-can-i-capture-the-current-directory-as-an-absolute-pathname-in-a-make-variab/3679235

In rare cases, like when using Cygwin, Make would get the wrong path,
will would in turn be mounted inside the docker container. Thus the
definition of the working directory is promoted to a new variable
inside the Makefile to allow for easier changes ...

Rationale: I've seen some really weird page breaks in listings, e.g. a page break after the caption or before the last (empty) line of a listing. Thus page breaks for listings are deactivated as default ...

Eisvogel uses H (HERE) if nothing else defined. This would prevent LaTeX
from using the usual floating figure placement ... In some (most?) cases
this leads to quite much whitespace ...

metadata.yaml contains now all metadata like author, the title of
the work and abstract/acknowledgement/...

all options regarding pandoc and the formatting of the document are
to be found now in the makefile.

pandoc would (try to) wrap lines at column 72 per default. when writing
the includes (title page, front matter, back matter), this could lead to
unwanted effects like merging a comment line and a macro definition ...

use chapter (left page header) or section (right page header) instead
of title of thesis ...

should fix #3

Squashed commit of the following:

commit 863f9d3ebd35daf47388156e22b30a46101d8ee4
Author: Carsten Gips <cagix@fh-bielefeld.de>
Date:   Tue Oct 15 08:19:55 2019 +0200

    metadata: add shorttitle variable

commit 42e61d1832578c837b8143fb45efc17e9e58f99f
Author: Carsten Gips <cagix@fh-bielefeld.de>
Date:   Tue Oct 15 08:19:19 2019 +0200

    frontmatter: fix typo