Implement editing of areas, like in vector drawing programs

[Sigra]

Implement editing of areas, like in vector drawing programs (such as Inkscape). This is needed for:
* Event unhide area
* Event conquer area
* Trigger building
* Future events and triggers.

Example:
The user is going to create a trigger building. He presses the mouse button where he wants the trigger, drags the mouse to set the radius and then releases the mouse. Then the options dialog is opened, where he can change the other options (player, building type, count). When he clicks OK in the dialog, the trigger is created and shown on the map with some text, such as "Trigger building: <name>". Holding the mouse pointer over it will show a tooltip with the properties (player, building type, count). Selecting it will allow moving it around by dragging the mouse. It will also show a handle that can be dragged to change the radius. Pressing Delete while the trigger is selected should delete it. Right-clicking on the trigger should bring up a context menu from which the trigger can be deleted or its options menu opened.

[SirVer (sirver)]

This is related to the discussion we had about areas in the editor. I created an empty blueprint for this and linked this bug report

[SirVer (sirver)]

Setting to incomplete for bug sweeping.

[Hans Joachim Desserud (hjd)]

This seems to talk about the pre-lua events, so I'm not sure how relevant this is.

Having a way of adressing sections or areas of the maps have certain uses though. Both for naming/implying significance (see bug 536542 for more on this), but also for triggering events in a campaign when a player exapnds into a certain area or events affecting multiple spots. Potentially a lot of work required to get this right, though, so it depends what we want to prioritize.

[SirVer (sirver)]

I think this is just an ancient form of 536542.