Construction of a new ContentItem is managed by ContentLocation.newContentItem. This is because there is a
parent-child relationship between ContentLocations and content items. To avoid having a content item reach back
into it's parent to add itself to the children list, you instead call the content location to construct a
content item. A content item cannot exist without a content location.
The behavior of this method depends upon it's write mode (defined only at construction).
If the write mode is WRITEMODE_KEEPVERSIONS, this method will create a new file on the disk, and add it to
it's internal list of files, and return an output stream.
If the write mode is WRITEMODE_OVERWRITE, this method will create an output stream and overwrite the existing
file on the disk if it's found, or will create the file if it doesn't exist.
If the write mode is WRITEMODE_APPEND, this method will append to the existing file on disk (if it exists), or
create it if it doesn't exist.
actionName - The name of the action that is obtaining the output stream.