move PivotTableRenderModel in base package and PivotCsvExporter in exporter package
add demo/db in gitignore
Merge remote-tracking branch 'upstream/master' into exporter_plugins

Conflicts:
	wicket-pivot/src/main/java/ro/fortsoft/wicket/pivot/PivotTableRenderModel.java
	wicket-pivot/src/main/java/ro/fortsoft/wicket/pivot/exporter/PivotCsvExporter.java
	wicket-pivot/src/main/java/ro/fortsoft/wicket/pivot/web/PivotPanel.java