Fixed missing namespace for FrontendUser
Added ProductCache model
Added relation information to tl_iso_productcache DCA
Moved method to find cache-applicable groups to the ProductCache model
Moved cache table locking check to model
The ProductCache model can truncate the cache
Improved variable name
Removed unnecessary global statement
Use model to find the current cache data
Added method to get product ID array from cache model
Improved method names
Use model to create product cache
CS
Use table name from model to lock tables
Purge product cache using the model
Merge branch 'feature/ProductCacheModel' into develop