Remove cache-manager dependency

[ryanricard]

Hi, @lammertw. I was reviewing this plugin and found it may not be providing the tiered priority caching benefits via cache-manager that you expect. You will find in the cache-manager source it is simply proxying the interface of your custom store (i.e. mongo_cache) without providing any in memory priority caching benefits (https://github.com/BryanDonovan/node-cache-manager/blob/master/lib/caching.js#L130). To leverage a tiered cache with cache-manager caching would need to be configured via its Multi Store api. This pull request removes the dependency of this plugin on cache-manager as it is not providing its intended value.

Please let me know if I am wrong or my understanding of the cache-manager source to be incorrect.

[lammertw]

Hi Ryan,

Thank you for the pull request. I'll investigate further and see how it can be best optimized in a few weeks. Right now I'm just a little bit too busy with other projects and private live to work on this project.