Generator able to generate assign-statement
Removed unnecessary this.
Changed StorageInformation.isConstant() to isMemoryAddress().

This reverts the meaning of the return value.
This allows us to not only use a StorageInformation without an address value
to represent a Constant, but also to represent a not yet set Jump-Point.
Added stubs for generating if and while
Added toString() to StorageInformation
Command stores whole StorageInformation to allow for changes after creation
Generator is able to generate code for if and while.

For now, a separate stack for storing information about jump addresses
is used, but this can be done in the usual addressStack.

Simplified command generation by passing each command
a StorageInformation object instead of an int and bool for constant/not
constant.