More clear attribute names for the manageContent tag

When reviewing ESSENTIALS-1108 I noticed that not all attributes of this tag do have very clear names. I suggest two changes to make it more clear for developers what their purpose is.

• rename the "document" attribute to "hippobean", which is more clear and in line with other tags like the hst.link tag
• to use "componentParameter" correctly you must check code or documentation. What you set with this parameter is the name of the parameter of a component that should contain the content path to the new document. What about renaming it to contentPathParameterName? I admit this name is a bit long but... it is very descriptive!