Add automatic stale cache cleaner

[aik099]

How it works now:

The file-based caching system is used where expiration of each cache entry is stored in corresponding file. The only way to invalidate cache is to access it and that will delete old cache and put new version of data in it. This results in lots of caches, that are not accessed frequently just laying around and taking valuable disk space.

How it should work:

1. create CacheManager::deleteExpired method, that will walk through all caches and delete ones, that are expired
2. add cache.expiration.checked config setting, that would store timestamp when expired caches were last cleared
3. as part of application initialization (once check if last expired cache time is missing or older than 1 day) and if it is run CacheManager::deleteExpired method and store new expired cache checking date