Mara-app

- Set two environment variables in activate script for preventing crashes related to multiprocessing on Mac
- Improve check for new package versions

- Remove last usages of dependency links
- Unpin pip version
- Add PyPi upload

**required changes**

- If you get the message `no such option: --process-dependency-links` while running `make update-packages`, then manually update `mara-app` and then run `make .copy-mara-app-scripts`
- Potentially also unpin `pip` in your deploy scripts

- Change MARA_XXX variables to functions to delay importing of imports
- Delay computation of navigation tree to the first time it's needed (in order to save load time)
- Remove dependency_links from setup.py to regain compatibility with recent pip versions
- Bump flask & mara db dependency
- Get working on Windows
- Fix bug in auto discovery of navigation entries
- Define navigation-bar enpoint in python code to make it mountable in a subfolder
with [`werkzeug.wsgi.DispatcherMiddleware`](http://flask.pocoo.org/docs/1.0/patterns/appdispatch/).


**required changes**

This release should be backward compatible with older other mara packages. However, when updating to packages that rely on this version of mara-app, changes to the application bootstrap process are required. Please have a look at the [`__init__.py` of the mara example project](https://github.com/mara/mara-example-project/blob/master/app/ui/__init__.py) for how to setup navigation and ACL.

For updating your own module's `__init__.py`, please have a look at the one of [mara-acl](https://github.com/mara/mara-example-project/blob/master/app/ui/__init__.py)

- Temporarily pin pip to version 18.1, because 19.0 removes --process-dependency-links option (`no such option: --process-dependency-links`)


**required changes**

- To get this change, manually upgrade `mara-app` to this version (git pull) and then run `make .copy-mara-app-scripts` in project dir. Remove `.venv` dir and rebuild with `make update-packages`.

- Enable python 3.7 (and future 3.x versions)

**required changes**

- Run `make .copy-mara-app-scripts` to copy [.scripts/install.mk](https://github.com/mara/mara-app/blob/master/.scripts/install.mk) to local project (that's part of `make update-packages`).
- If not possible, copy manually.

- Move auto-migrate feature to mara-db package
- cope with absense of local git checkout in layout._current_git_commit
- Wipe incompatible local copies when pip installing packages
- Fix bug in appending git commit to js file url