Add the Move Parallel Tool

[lpechacek]

Although the Move Parallel tool does not behave perfectly in every situation (shape distortion on small curves and bevel-join-like corner cuts on sharp corners), it works fine on "sensible" shapes. This is still an improvement over the current state where the best approximation of this tool is the Line Edit tool or tricks with helper double lines.

[dl3sdo]

One small observation: although the Move Parallel tool can only be activated once an appropriate object has been selected, it stays activated once the object becomes unavailable (e.g., has been moved to another map part, has been deleted or it's underlying symbol has been deleted). That's not a big issue since you can deactivate the tool by choosing another tool.

[lpechacek]

One small observation: ...

Thanks for testing! I've aligned the new tool behavior with the other tools on this front.