This issue complements issue 324, which allows using the GXP "AddLayers" 
related widgets for adding new Layers via preconfigured or user-supplied 
WMS/WFS/TMS Capabilities URLs.

This issue encapsulates the work related to integrating and enhancing the GXP 
"FindLayers", which is based on CSW (Catalogue Service for the Web). In this 
scenario a user can issue search strings to search Metadata stores via CSW for 
data and services like WMS/WFS/WMTS. 

GXP has an existing implementation but very much based on a local interaction 
with a well-defined Metadata server. See example 
http://gxp.opengeo.org/master/examples/catalogue.html (do + button top left, 
the Find Layers and search for e.g. "water"). But the example, interacting with 
pycsw does not render valid WMS references. This also touches on the main issue 
interacting with a CSW: the protocol payload is too broadly defined, allowing 
many different formats and encodings...

We'll try at least and provide enhancements in the user and protocol 
interactions. We'll try to backport these to GXP via GitHub and an issue there: 
https://github.com/boundlessgeo/gxp/issues/235