Equation library to store generated equations.

Generated equations should automatically be saved in a library. When the user creates a new equation, current equation is saved in library and a new one is created. Thus, no buttons to save, or save as. Equations can only be exported or imported (see the blueprint for functionality-export-import) or drag and drop.
Also, the user should have the possibility to remove equations from the library and search it (see functionality-tags blueprint).