Bug 1249774: Add SecurityMiddleware and settings for HSTS
Bug 1249774: Add SecurityMiddleware and settings for HSTS

Also add setting for XSS filter header. All are disabled by default
so that we can turn them on and test.

gerv/bedrock,jgmize/bedrock,MichaelKohler/bedrock,Sancus/bedrock,ericawright/bedrock,craigcook/bedrock,sylvestre/bedrock,kyoshino/bedrock,alexgibson/bedrock,mkmelin/bedrock,pascalchevrel/bedrock,kyoshino/bedrock,pascalchevrel/bedrock,ericawright/bedrock,jgmize/bedrock,sgarrity/bedrock,schalkneethling/bedrock,mozilla/bedrock,TheoChevalier/bedrock,sylvestre/bedrock,schalkneethling/bedrock,hoosteeno/bedrock,pascalchevrel/bedrock,ericawright/bedrock,sylvestre/bedrock,flodolo/bedrock,MichaelKohler/bedrock,craigcook/bedrock,alexgibson/bedrock,mkmelin/bedrock,hoosteeno/bedrock,glogiotatidis/bedrock,jgmize/bedrock,CSCI-462-01-2017/bedrock,flodolo/bedrock,gerv/bedrock,mkmelin/bedrock,flodolo/bedrock,hoosteeno/bedrock,sylvestre/bedrock,glogiotatidis/bedrock,mkmelin/bedrock,MichaelKohler/bedrock,mozilla/bedrock,sgarrity/bedrock,hoosteeno/bedrock,ericawright/bedrock,Sancus/bedrock,CSCI-462-01-2017/bedrock,Sancus/bedrock,glogiotatidis/bedrock,TheoChevalier/bedrock,gerv/bedrock,craigcook/bedrock,sgarrity/bedrock,alexgibson/bedrock,kyoshino/bedrock,kyoshino/bedrock,glogiotatidis/bedrock,jgmize/bedrock,mozilla/bedrock,pascalchevrel/bedrock,craigcook/bedrock,TheoChevalier/bedrock,gerv/bedrock,MichaelKohler/bedrock,alexgibson/bedrock,CSCI-462-01-2017/bedrock,schalkneethling/bedrock,mozilla/bedrock,Sancus/bedrock,flodolo/bedrock,sgarrity/bedrock,CSCI-462-01-2017/bedrock,TheoChevalier/bedrock,schalkneethling/bedrock