refactor: move xmodule folder to root

- Moving xmodule folder to root as we're dissolving sub-projects of common folder in edx-platform
    - More info: https://openedx.atlassian.net/browse/BOM-2579
- -e common/lib/xmodule has been removed from the requirements as xmodule has itself become the part of edx-platform and not being installed through requirements
- The test files common/lib/xmodule/test_files/ have been removed as they are not being used anymore

xmodule/modulestore/edit_info.py

@@ -0,0 +1,103 @@
+"""
+Access methods to get EditInfo for xblocks
+"""
+
+
+from abc import ABCMeta, abstractmethod
+
+from xblock.core import XBlockMixin
+
+
+class EditInfoMixin(XBlockMixin):
+    """
+    Provides the interfaces for getting the edit info from XBlocks
+    """
+    @property
+    def edited_by(self):
+        """
+        The user id of the last user to change this xblock content, children, or settings.
+        """
+        return self.runtime.get_edited_by(self)
+
+    @property
+    def edited_on(self):
+        """
+        The datetime of the last change to this xblock content, children, or settings.
+        """
+        return self.runtime.get_edited_on(self)
+
+    @property
+    def subtree_edited_by(self):
+        """
+        The user id of the last user to change content, children, or settings in this xblock's subtree
+        """
+        return self.runtime.get_subtree_edited_by(self)
+
+    @property
+    def subtree_edited_on(self):
+        """
+        The datetime of the last change content, children, or settings in this xblock's subtree
+        """
+        return self.runtime.get_subtree_edited_on(self)
+
+    @property
+    def published_by(self):
+        """
+        The user id of the last user to publish this specific xblock (or a previous version of it).
+        """
+        return self.runtime.get_published_by(self)
+
+    @property
+    def published_on(self):
+        """
+        The datetime of the last time this specific xblock was published.
+        """
+        return self.runtime.get_published_on(self)
+
+
+class EditInfoRuntimeMixin(metaclass=ABCMeta):
+    """
+    An abstract mixin class for the functions which the :class: `EditInfoMixin` methods call on the runtime
+    """
+
+    @abstractmethod
+    def get_edited_by(self, xblock):
+        """
+        The datetime of the last change to this xblock content, children, or settings.
+        """
+        pass  # lint-amnesty, pylint: disable=unnecessary-pass
+
+    @abstractmethod
+    def get_edited_on(self, xblock):
+        """
+        The datetime of the last change to this xblock content, children, or settings.
+        """
+        pass  # lint-amnesty, pylint: disable=unnecessary-pass
+
+    @abstractmethod
+    def get_subtree_edited_by(self, xblock):
+        """
+        The user id of the last user to change content, children, or settings in this xblock's subtree
+        """
+        pass  # lint-amnesty, pylint: disable=unnecessary-pass
+
+    @abstractmethod
+    def get_subtree_edited_on(self, xblock):
+        """
+        The datetime of the last change content, children, or settings in this xblock's subtree
+        """
+        pass  # lint-amnesty, pylint: disable=unnecessary-pass
+
+    @abstractmethod
+    def get_published_by(self, xblock):
+        """
+        The user id of the last user to publish this specific xblock (or a previous version of it).
+        """
+        pass  # lint-amnesty, pylint: disable=unnecessary-pass
+
+    @abstractmethod
+    def get_published_on(self, xblock):
+        """
+        The datetime of the last time this specific xblock was published.
+        """
+        pass  # lint-amnesty, pylint: disable=unnecessary-pass