Created PivotConfig container class to store / restore the state of the
PivotModel in a stable format. What format exactly is used is not
specified.
Forgot the copyright header
PivotConfig: Basic UI for store/restore of the configuration

Also did a small bugfix on the interface of IPivotConfigStorage. The UI
is functional, but not really pretty at the moment.
Demo: Sample Session Storage for the Pivot Config

Build a sample IPivotConfigStorage, which stores everything in the
session. The config is serialized using Gson.
Renamed PivotConfigStorePanel => PivotConfigStoragePanel
Renamed PivotConfigStorageSession => PivotConfigSessionStorage
Merge pull request #13 from rototor/pivot_config_storage

Pivot Table Config Storage