Global KnowledgeBase access

I think the current KB (or `angr.Project`) should be globally accessible, either as a global var or through a globally-accessible workspace property. The `DisassemblyView` only has it through the `cfg`, which doesn't exist right off the bat. In other places, like the functions table, I've had to hack in a new property.

For example, I'm writing a KB plugin that stores information per instruction or per function and I lookup function/instruction information in the plugin to change the background highlight color in the disassembly and/or function table widget.

EDIT: Ditto for making the current project accessible through the Python console.