Try to unify grabbers in a more generic way

[elboletaire]

After adding support to tcbscans.com I realized grabbers could be created in a more generic way, rather than having grabbers almost for every single site.

The new PlainHTML grabber could be a good starting point. On the other side, the current TCB grabber could be renamed to Ajax, since all its behavior works around ajax calls.

This new PlainHTML is actually a copy of manganelo (removing ajax functionality recovered), so most of the sites from the manganelo grabber could be moved to the PlainHTML one.

I think it'll be better to add a new layer in the grabber architecture that handles the different selectors, and leave the grabbers as more generic interfaces. Doing this, in the future adding new sites should be as easy as just setting the proper grabber and define the selectors and other required identifiers for that grabber.