more Automation Points options

[tjingboem]

for moving about the Automation Points in Single Line Mode, for example:

• use Ctrl + click to create AP that stays on exactly the same X axis. Then: the first movement up or sideways will stay on the same X or Y axis.
  What happens now is that when you set a AP between other APs, this new AP is created somewhere on that spot
• use Shift + select to select several APs so that all the selected APs can be moved around a bit

[kunstmusik]

I have implemented the ctrl-drag option that limits editing to a single direction. The use of ctrl can be used after dragging starts as well.

I found that shift-selection of points is already supported for automation editing in single-line mode (via marquee).

These changes will be available in 2.6.1_test3.