====== Proposal: Nodes property windows enhancement ======

===== Current situation =====

in the current situation inside the node editor there is a properties panel
(press 'n'-key). This pabel displays some information about the node,
backdrop and grease pencil. The UI of the property panel is typically
vertical oriented. Nodes in the other hand are not oriented in a direction.
Both area's are draw via the same draw function.

With some nodes this will create not user-friendly UI. Try the
color-balance for instance). The 3 color circles are drawn next to each
other, it would be better to draw them below each other.

When creating more complex nodes you don't want to display all handles in
the node-panel and in the properties panel. For instance finetuning handles
you only want to appear in the property panel to reduce place in the node
itself.

===== Proposal =====

My proposal is to separate the draw functions of the property panel and the
node panel.
When no special draw function is created for the property panel, the draw
function of the node will be used as 'fallback'

===== Impact =====

==== BKE_node.h ====

add a new uifunc (called uifuncbut) to the bNodeType struct. The definition
is the same as the uifunc.

==== node_buttons.c ====

if the uifuncbut is set, call it. currently calls the uifunc method

==== drawnode.c ====

static void node_composit_set_butfunc(bNodeType *ntype). set the uifuncbut
function where needed. When at the end of the method uifuncbut is still
empty, set uifuncbut to the uifunc.