Refactor cache usage

[dennisvang]

Custom cache implementations are used throughout the FDP app.

For example:

• CacheConfig
• FormsAutocompleteCache
• ResourceDefinitionCache
• ResourceDefinitionTargetClassesCache
• SearchFilterCache
• SettingsCache

Probably it would be more robust, and clearer, to use Spring's annotation-based caching integration, using e.g. @Cacheable, etc.

Here's at least one problem with the current implementation:

• The ResourceDefinitionCache getters are marked as possibly "not needed anymore".
  Actually it looks like both getter query the repository directly instead of relying solely on the cached data:

  FAIRDataPoint/src/main/java/org/fairdatapoint/service/resource/ResourceDefinitionCache.java

  Lines 74 to 76 in e746e9a

  	public ResourceDefinition getByUuid(UUID uuid) {
  	// TODO: not needed anymore?
  	return resourceDefinitionRepository.findByUuid(uuid).orElse(null);

  FAIRDataPoint/src/main/java/org/fairdatapoint/service/resource/ResourceDefinitionCache.java

  Lines 79 to 80 in e746e9a

  	public Set<ResourceDefinition> getParentsByUuid(UUID uuid) {
  	// TODO: not needed anymore?