timezone select (#743)

* add config option for timezone to SettingsController

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

* add timezone config to SettingsService

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

* add timezone input in settings area

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

* connect timezone setting to actual calendar grid

Signed-off-by: Georg Ehrke <developer@georgehrke.com>