Split the library implementation into a set of static libraries

[d1vanov]

The idea is to restructure libquentier into a single shared library which encapsulates the public interfaces and a set of static libraries with the actual implementation of these public interfaces. The upside of this would be the ability to use dependency injection more freely and thus write more meaningful unit tests. The only downside is that, well, it's a sufficient amount of work to be done. Probably I won't be doing this in the nearest future but at some point I'd like to consider it.