[EntitySeed] Compatibility fixes

Some fixes to enable compilation of the gridcheck

- make constructors public
- add default constructor
[Entity] Add intersection iterator access methods to make gridcheck happy

This is kind of pointless, as they will go away directly after 2.3, but
without them, it's not possible to build the gridcheck.
[Git] Ignore "compile" helper binary from autotools
[SubDomainGrid] Fix a final occurrence of bitrot in subdomain intersection iterator

Missed an iterator dereferencing and method rename during the recent
cleanup...
[testpartitioning] Set up grid manually (without GridPtr hackery)
[testpartitioning] Fix compilation failure

Apparently you can't assign an iterator to an EntityPointer during
construction. Well, broken engine concept, so I don't really care...
[Git] Enable whitespace hook
[Documentation] Massive documentation update including addition of proper license information

This patch finally adds something like a minimum amount of
documentation, providing

* links to a canonical source (GitHub)
* proper license information (GPLv2 with template exception and LPGLv3
  or later)
* a list of contributors
* release notes
* a sane versioning scheme (reuse first two components of compatible
  DUNE release)

The documentation has been formatted in GitHub-flavored Markdown to
enable nice formatting on the GitHub site.
[Whitespace] Add missing newline at end of file
[Tests] Disable ancient GRIDTYPE hack for testpartitioning