Extend JcrPath annotation to allow linkpicker to refer docs outside the channel's content scope

HST components use JcrPath annotation to enable a component parameter can be set by using linkpicker. It could refer to documents inside the channel's content scope.

Motivation: in some projects, we need refer documents in the other channels (i.e. outside the channel content scope). An extension in JcrPath to configure which is the picker root path would solve this requirement.

Approach:

• Add the "pickerRootPath" parameter in JcrPath with the empty string default value (JcrPath:52)
• If pickerRootPath is set explicitly, the link picker use this parameter as the root path. Otherwise, it uses the channel mount content path (currently) as the root path (ParametersInfoProcessor:89-92).