When portainer is restarted the user's session is invalidated and as
soon as they start clicking around they will be logged out. This PR does
two additional things when this happens.
1) We trigger a browser page reload which will force the client the grab
the latest version of our js, css, etc. Previously if a user updated
portainer, but never clicked the browser's refresh button they would
never see new css changes.
2) We also set "cache-control no-cache" on the index.html header. Since
portainer is an SPA and the the index.html is very small it makes
sense to avoid letting the browser cache it so that the user is
always given the latest version when the above reload is triggered.
7b806cf586