Add util to make current year and month strings available

The create content feature in the Channel Manager makes it possible to create new documents at a certain default path. An example are the year/month based paths. Instead of adding script tags to JSPs to calculate these, components should provide these strings.

The utility can be in org.onehippo.cms7.essentials.components.utils.ComponentsUtils and can be used by components that need it: the EssentialsNews- and EssentialsEventsComponent.