Transform `SpecfileClass('Specfile 2.0')` into its own module

[ingvagabund]

TODO

• implement new SpecModel class encompassing current SpecfileClass('Specfile 2.0')
• implement new SpecModelGenerator class transforming the raw spec file into the new SpecModel class
• move and refactor all relevant procedures/functions under model_methods.py and model_2_methods.py under the SpecModelGenerator class

Story:
The SpecModel is the first product that is consumable outside of the library. One can either transform an instance of the class into a spec file (no transformation to SpecFileV1) or queue it for other processing like transformation into GoSpecModel class (yet to be implemented). The SpecModel provides various manipulation operations such as:

• add/remove subpackage
• add/remove subpackage buildtime/runtime depedency
• edit summary of a subpackage
• add/remove tests to/from %check section
• add/edit/remove macros/tags
• other

[ingvagabund]

Partially implemented through #11