convert/mediafile: no longer export sound file list
game: Made shared_ptrs into unique_ptr and added an implementation of make_unique

Some objects that were represented in the engine were held in shared_ptrs,
despite having a single owner and a well-defined lifetime.
I moved them to unique_ptrs so that it was clear that they had a single owner,
and so that it was obvious when they were released.
I also added an implementation of make_unique from c++14 to facilitate the use of unique_ptrs
Merge pull request #175 from schets/unique_ptrs

Moving uneeded shared_ptrs to unique_ptr
py: better pep8 compliance

executed: pep8 --ignore=E251,E221,E501,E241 py/
codecompliance: added style checking for python
ci: install pep8 python package
Merge pull request #177 from TheJJ/pep8

better pep8 compliance for py/
Merge branch 'master' into arrows_fired

Conflicts:
	cpp/game_main.cpp
	cpp/unit/ability.cpp
	cpp/unit/ability.h
	cpp/unit/producer.cpp
	cpp/unit/producer.h
	cpp/unit/unit.cpp
	cpp/unit/unit.h
	cpp/unit/unit_container.cpp
	cpp/unit/unit_container.h
	py/openage/convert/gamedata/unit.py