Parts management : create / add / update sub parts in product structure
#65
Merge branch 'subpart-creation' into dev

Conflicts:
	docdoku-server/docdoku-server-web/src/main/webapp/less/product-structure/content.less
	docdoku-server/docdoku-server-web/src/main/webapp/less/product-structure/menu.less
	docdoku-server/docdoku-server-web/src/main/webapp/less/product-structure/unknown.less