Improve HTTP caching

[ChristophWurst]

• More immutable cache headers
• Cache itinerary responses
• Cache quota
• Cache contacts integration lookups
• Cache recipient auto completion lookups
• Cache auto config lookups

How to test

1. Open the app with master
2. Open a mailbox
3. Open a thread
4. Open another thread
5. Go back to the first thread -> this should feel a bit slow

Then switch to this branch and do the same steps.

It should go without saying but don't have your browser cache disabled or you won't see a difference.