Refactor node

[wawuwo]

Hi!

I've refactored the Node class to address the problem from #748.

@dsm seems to be working on the same issue in #832, but in a broader scope, I hope this piece doesn't interfere with his work. Anyway some synchronisation may be required upon merging (if it happens).

List of changes:

• Remove dependency on Q3PtrList (most important)
• Hide implementation details (in particular make private the container used to actually store connected elements)
• Completely new API
• Formatting and code structuring
• Move 'Conductor' from element.h to a separate header file (not related to Node, just sorting things out)

I've done some tests on my side, in particular:

• lay horizontal wire, lay vertical wire
• lay two-segment (L, Г, etc.) wire
• lay multiple-segment wire, i.e. chain of wires (click, move cursor and click, move cursor and click, and so on.)
• connect wire to a component
• start new wire from a middle of existing wire
• end new wire in a middle of existing wire
• move connected component around
• delete connected wire segment, delete connected component

All described above went smoothly, but one cannot be 100% sure; some nasty bug is probably hiding waiting for perfect conditions to occur :(

[dsm]

@ra3xdh, @wawuwo, Hi, some changes related but my work not done properly, I just got back from holiday, I choose this way for Connections in node.h std::list<std::weak_ptr<Element> > Connections; we have too many raw pointer in qucs-s so we should use smart pointers for refactoring. We need to refactor thousands of lines of code :(

in sweepdialog.cpp I removed this lines not confusing for loop variables:

Node *pn;
Element *pe;

[ra3xdh]

I have tested this and didn't found issues with schematic editing, save, load. I am merging this.

[ra3xdh]

@wawuwo I have found a crash related to this PR. It is not possible to place the device on wire. Normal device connection works as expected. The placing of one device port on wire works as expected. Steps to reproduce:

• Try to place any device over the wire. Usually device should be connected to the wire.
• Application crashes at Schematic::insertComponentNodes

Could you have a look?

[wawuwo]

@ra3xdh,I am almost certain that the reason is that connected elements are being removed from node's internal std::list in deleteWire while iteration over this list (indirectly, through Node's begin() and end()) is in progress in insertComponentNodes, and it breaks the iterator.

I don't have a solution right now, need some time to think what could be done