convert license headers to SPDX

Includes license review of 3rd-party files, adding missing upstream
headers, and moving the UNSW OZPLB license into its own file rather
than replicating it in the header.

Pass style.py -f flag only if filter file exists

This keeps style.py from trying to open a nonexistent .stylefilter.

Make style cleanups.

* misc/style-c.sh: Use the shell's && instead of "test -a", which is now
"obsolescent" per POSIX 2018 (see
http://pubs.opengroup.org/onlinepubs/9699919799.2018edition/).

* misc/style-all.sh: Indent branches of if-then-else conditional.

* misc/style-c.sh:
* misc/style-py.sh: [English] Prefer "in place" to "in-place" when not a
attributive modifier.

* misc/style-changed.sh:
* misc/style.sh: [English] Give comment sentences terminal punctuation.

* misc/cobbler:
* misc/style-c.sh:
* misc/style-cmake.sh:
* misc/style-py.sh:
* misc/style.sh: Standardize whitespace around CSIRO header.

misc: increase functionality of style.sh

- split style.sh into style-c.sh and style-cmake.sh
- add style.py, which passes files based on extension to the correct
style tools and ignores files specified in a .stylefilter file (only at
the top level)
- style.sh now calls style.py and expects a list of files
- add style-changed.sh, which styles all changed files in a git repo.
- add style-all.sh, which styles all files in directories passed to it

Add tools for formatting cmake

- add an invocation to cmake-format to style.sh. We pass command line
arguments as a default style, which can be overriden by providing a
.cmake-format.json in directories that this tool is invoked from.

misc/style.sh: minor tweaks

- use find to collect files to avoid following symlinks
- use #!/bin/sh over bash

misc: Added an astyle script

Added a simple script to run astyle on a given directory.
This is functionality ported from the Kbuild system.
To invoke the user runs:
"misc/style.sh -s=/dir/to/src".