Improved folding and connector popup

Hi all

Thanks for the great work with FreePlane! I use it every day. In the forum, I made some suggestions some time ago [1]. Today I made an attempt to implement them.

1. When clicking a connector, the popup was displayed as normal window. I use Linux with a tiling window manager (i3wm), so the popup screwed up the screen layout. I have replaced the javax.swing.Box by a javax.swing.JPopupMenu (baabf74).

2. e4af8a7 automatically closes the popup when the "Goto:" button was clicked; this seemed more natural to me. I am not sure what the code in freeplane/src/org/freeplane/features/link/LinkController.java, line 235ff, does :-(. Could you please help me get this bit right too?

2. Folding used to work (in 1.1.3) by double clicking into the node. In the current version, only single clicks toggled the fold. I have changed this in 3c30077.

3. Also in 1.1.3, the folding was part of the undo/redo history. This was gone since 1.2.x. I have added it back (e1ee218).

I would appreciate if you merge my changes into your master. Thanks a lot!

Regards,
Benedikt

[1] https://sourceforge.net/apps/phpbb/freeplane/viewtopic.php?f=1&t=783&p=3835#p3835