Respect config options constrain/constrainHeader.

The draggeing behaviour of instances of Ext.window.Window
usually can be configured with e.g. `constrain` or `constrainHeader`.
Since our gx_popups usually start pinned to a location and get their
dragging behaviour added when they are unpinned, those config options need
to be passed to our dynamically created dd-object.
Optionally constrain gx_popup in example.
Adjust win positioning as suggested by @chrismayer
Merge pull request #166 from marcjansen/popup-constrain

Respect config options constrain/constrainHeader (r=@chrismayer)
Add license header to PrintPageField.js & View.js.
Adjust copyright to 2013.
Merge pull request #167 from marcjansen/copyright-year

Adjust the copyright year
Update src/GeoExt/tree/LayerContainer.js

Removed error in API-Docs example code