Throw exception is template does not exist.
generalize ProcessorDependency from AbstractProcessor to Processor.

Allow adding customInputs, this is for the CustomDependencies implementations that will come in next commit
Add option for processors to define dependencies based on the processors in the current template.

This is require by MergeDataSourceProcessor because its required inputs depends on the configuration so they can't be statically defined like scalebar depending on createmap.
Added test for getTemplate() in configuration