fix(import): forgive invalid flowElements

Instead of failing hard when we parse invalid flow elements (i.e.
TextAnnotation) we log a warning that may be handled by the diagram
import.

Related to #74
chore(Gruntfile): use debug:true during karma run
fix(LabelEditingProvider): work around old WebKit incompatibility
test(bpmn/draw): correct test case
feat(modeler): add createDiagram API

Related to #4
test(zoomScroll): add basic test
(feat) refactoring of navigation code
feat(navigation) fixed touch based scrolling
feat(navigation): improved touch zooming
chore(Viewer): adjust SVG export for group zooming