Hoader throws java.lang.AssertionError for the case of missing cache to apply

[danicheg]

The default behavior of the plugin implies that caches for all SBT projects exist for applying and throws an exception if cache not found. For multi-project builds, it means adding a new project (e.x. for case a monorepo) will lead to failed incremental build at CI.

I propose a setting allowApplyingEmptyCache which allows changing exceptional behavior in the case of the missing cache to apply. See #72. Nevertheless, if the setting not defined by the user the default exceptional behavior would remain.