Cache Overview Service and invalidate when any TechStack is added/modified
Add Unique indexes to Slugs
Add init-data directive and load static config data once on load
Always call overview service on each refresh
Merge remote-tracking branch 'origin/master'

Conflicts:
	src/TechStacks/TechStacks.ServiceInterface/TechnologyStackServices.cs
	src/TechStacks/TechStacks.ServiceModel/TechnologyStacks.cs
	src/TechStacks/TechStacks/js/tech/controllers.js
allow external links to /auth/xxx through