The add property dialog (introduced by the LinkMerge) previously
showed "Document" which is confusing. The edit box is there
to provide an explanation on the new property, that is,
"Documentation".
Also improve the tooltips. Also change "Append" to "Prefix"
in the checkbox as it's more clear that the `Group` is added
at the beginning to form the full name of the property.
* Display property from linked object, colored green,
* Change DlgPropertyLink to support external linking and sub-object
selection
* Improve large selection performance by using a timer
* Improve TAB key behavior in property editor
* Add context menu to show hidden properties, change property status,
set expression on any and property, and add/remove dynamic properties
* Optimize expression completer model construction, as the original
implementation gets prohibitively slow for moderate number of objects.
