getBestPlugin: allows to get all possible plugins for a given file extension
change init_logging

* init_logging is now called in the constructor of Formatter
* Formatter is instantiated inside Core
tuttleHost: Graph.compute choose the internal MemoryCache

Allows to choose the internal MemoryCache to use during the compute.

* Use IMemoryCache
* Store a link to the memoryCache to use in ProcessVertexData