Cache results of `getTimezoneNameNoLocationSpecific`
Cache results of `getTimezoneNameNoLocationSpecific`

`getTimezoneNameNoLocationSpecific` is a very expensive operation and previously a simple looped time conversion (1000x) required more than two seconds to execute.

At ownCloud we use such date conversion actions pretty often and repeatedly and thus listing a folder with more than 20k files took more than 3 seconds longer just due to this single method.

Remo/punic,Remo/punic