Remove HTML purifier cache

Disable the cache since ownCloud has no really appcache
TODO: Fix this - requires https://github.com/owncloud/core/issues/10767 to be fixed
Use Cache.DefinitionImpl instead of Cache.DefinitionCache
correct Core to Cache
Merge pull request #260 from owncloud/remove-cache

Remove HTML purifier cache
reintroduce All Accounts view and set as default
add account email label
remove account switcher
improve styling for new message button now that account switcher is gone