Fix pytest warning about duplicate name when running tests

When running pytest on kubuntu 16.04 the following warning was displayed:

    $ python3 -m pytest -v
    ...
    ./manuskript/load_save/version_1.py:319: \
    UserWarning: Duplicate name: 'outline/0-Folder/0-Text-3.md'
      zf.writestr(filename, content, compress_type=compression)

The error was tracked down using the following pytest invocation:

    $ python3 -m pytest -v -W error::UserWarning

This invocation showed 4 occurrences similar to the following warning:

    self = <zipfile.ZipFile filename='/tmp/tmpgs_sjpzr.msk' mode='w'>
    zinfo = <[AttributeError("compress_size") raised in repr()] \
    ZipInfo object at 0x7f3cc0124588>

        def _writecheck(self, zinfo):
            """Check for errors before writing a file to the archive."""
            if zinfo.filename in self.NameToInfo:
                import warnings
    >           warnings.warn('Duplicate name: %r' % zinfo.filename, \
                stacklevel=3)
    E           UserWarning: Duplicate name: 'outline/0-Folder/0-Text-3.md'

These warnings arose in the following 4 tests:

  - test_references
  - test_autoLoad
  - test_loadExportWiget
  - test_loadImportWiget

The cause of the issue is that in manuskript/tests/conftest.py, the
mainWindow::closeProject() method is called to close the project, but
the project was never loaded.  This meant the zip file setting
defaulted to True, when in fact the Acts sample project is not stored
in a single zip project file.

Fix by removing the call to MW.closeProject() before the project is
loaded.

manuskript/tests/conftest.py

@@ -66,7 +66,6 @@ def MWSampleProject(MW):
     import shutil
     shutil.copyfile(src, tf.name)
     shutil.copytree(src[:-4], tf.name[:-4])
-    MW.closeProject()
     MW.loadProject(tf.name)
     assert MW.currentProject is not None