Clarify the text of visualeditor-dialog-media-position-checkbox

Change "Wrap content with this item" to
"Wrap text around this item".

The content is usually text, so using "text" should be
clearer and easier.

And saying "wrap content with this item" may be understood
as if the text is wrapped inside the content, which
is not the case.

Change-Id: I6b9e8767d38eb39ae4d671f452660db6b89fe3d9