[LWFXEF] More options for javafx editors
More options are needed in order to match the previous UI.
This issue complement #3889 which refers only to text.
- Allow fixed colors to fill an element. See e.g. platform architecture in the old UI. ECUs are green/yellow, buses are green/white
- Allow to change the position of the icon. Currently I managed center the text (name) of a rectangle, but the icon remains always on the left.
- Allow to "decorate" rectangles. E.g. in the old UI, generic ECUs have dots in the corners
- Allow to create a channel by selecting the input connector and moving to mouse to the output connector.
- Allow to reconnect a link: i.e. change the end-point of a link
- Allow to move an existing connector using the keyboard arrows. Currently it works for rectangles, but not for anchors.