Introduce LexiconStorageFactory that accepts a config instance.

First version of this solution will look at a single config parameter it treats as an enum:

SpeechoidOnly
Handler_Wiki_Speechoid
Handler_WanCache_Speechoid

Add todo comments that in the future multiple config variables for local and remote lexicon class names might be a good idea, in case we implement other storages (e.g. WikiBase lexems or what not)