Add example for loading features via ProtocolProxy

Added another example to show how to use a GeoExt.data.proxy.Protocol to
load features into a FeatureStore and sync this store with a vector-layer.
Harmonized white spaces
Minor style adaptions.

According to the comments by @marcjansen some minor style adaptions are
added by this commit.
Merge pull request #318 from chrismayer/example-protocol-proxy

Add example for loading features via ProtocolProxy
Remove unused variable in example.