Additional navigation in source

[kowalski]

• Step into currrent function (if we are on the JUMP)
• Step out of current function (should go to JUMPDEST marked as o)
• Step over current function
• Jump out of current function

For the moment we only have navigation

• next opcode (arrow down)
• previous opcode (arrod up)

So ideally we would hook this new navigation to some keystrokes too