🔧 Fix broken links in intro to docker slides

Closes #622

I recovered some of the case studies from the internet
archive, and removed the other links.

slides/containers/Docker_Overview.md

@@ -113,22 +113,16 @@ class: pic
 ## Results
 
 * [Dev-to-prod reduced from 9 months to 15 minutes (ING)](
-  https://www.docker.com/sites/default/files/CS_ING_01.25.2015_1.pdf)
+  https://gallant-turing-d0d520.netlify.com/docker-case-studies/CS_ING_01.25.2015_1.pdf)
 
 * [Continuous integration job time reduced by more than 60% (BBC)](
-  https://www.docker.com/sites/default/files/CS_BBCNews_01.25.2015_1.pdf)
+  https://gallant-turing-d0d520.netlify.com/docker-case-studies/CS_BBCNews_01.25.2015_1.pdf)
 
 * [Deploy 100 times a day instead of once a week (GILT)](
-  https://www.docker.com/sites/default/files/CS_Gilt%20Groupe_03.18.2015_0.pdf)
+  https://gallant-turing-d0d520.netlify.com/docker-case-studies/CS_Gilt_Groupe_03.18.2015_0.pdf)
 
 * [70% infrastructure consolidation (MetLife)](
-  https://www.docker.com/customers/metlife-transforms-customer-experience-legacy-and-microservices-mashup)
-
-* [60% infrastructure consolidation (Intesa Sanpaolo)](
-  https://blog.docker.com/2017/11/intesa-sanpaolo-builds-resilient-foundation-banking-docker-enterprise-edition/)
-
-* [14x application density; 60% of legacy datacenter migrated in 4 months (GE Appliances)](
-  https://www.docker.com/customers/ge-uses-docker-enable-self-service-their-developers)
+  https://www.youtube.com/watch?v=Bwt3xigvlj0)
 
 * etc.