Merge pull request #19 from a0x77n/dev

Format and organize imports.
Add package for universal graph utilities.

Move existing files accordingly.
Introduce base classes for graphs.

These classes are designed to provide basic functionalities for
inheriting classes.
Simpify control flow graph.

The control flow graph extends 'AbstractTwoWayGraph' now. Adapt all
dependent classes to work with the new interface.
Simplify control dependece graph.

The control dependence graph extends 'AbstractGraph' now. Adapt all
dependent classes to work with the new interface.
More work on tutorial for workshop.
Merge branch 'dev' of ssh://github.com/fabsx00/joern into dev
Merge pull request #20 from a0x77n/graphutils

Graphutils
Fix #21.
Fix #22 : IncDecOp now also have USE/DEF edges just like AssignmentExprs. Prior to this commit, they were missing USE-edges while DEF-edges were already present.
Fix control flow graph.

Continue and break statements are handled as jump statements now.