Implements caching for all catalog clients

Includes full tagging and expiration dates
Deletes corresponding cache entries after saving an item or its associations
Fixes type of associated texts for product attributes
Deprecates isCachable() method as caching is done internally
Fixes retrieving associated texts, media, etc. for all items
Fixes bugs uncovered while testing for tags
Implements tests for cache tags and expiration dates
Improves caching for catalog stage client and adapts interfaces of remaining catalog clients
Adapts account clients to modified interfaces
Adapts basket clients to modified interfaces
Adapts checkout clients to modified interfaces
Adapts common html clients to modified interfaces
Adapts forgotten methods to new interfaces
Adapts email html clients to new interfaces
Removes unnecessary parameters for _getSubClients() in catalog clients
Adds slicing to cache manager when searching for items
Rearranges execption handling to test getHeader() better
Improves caching for last seen items
Improves exception handling
Extends key column to show the complete key