Blender Git Loki

UI: Draw real node sockets for node-input buttons and left-align them

Couple of reasons for this:
* Makes it easier to understand that and how these buttons map to nodes.
* These buttons represent node inputs, so it makes more sense to have the icons
on the left.
* We'd like to show the usual decorators on the right, but having two circles
for different purposes next to each other would be confusing.

Also respects the socket shape. So if a diamond shape is used for example, the
properties show that too.

I'm not sure if the previous icon textures were cached, either way this method
doesn't use the caching. So this adds a draw call for every socket icon which
is a bit annoying, but probably neglectable. Would be better if we'd use proper
icon textures or batches, but that's a separate change.

Differential Revision: https://developer.blender.org/D7409

Fix wrong use of heading in Preferences

Use row headings and correct alignment for more Symmetry panels

Use column header for Armature Viewport Display panel.

Draw node socket icons in properties using real node socket shape/color

Fix error in previous commit

I unintentionally changed the size of checkboxes, should be back to the
old size now.

Change padding around checkboxes

Two changes:
* Reduce padding between checkbox and text. That makes it clearer what
the checkbox belongs to if there's also a column heading in front of
the checkbox.
* Don't add padding on the left side of checkboxes. That makes them line
up better with items above and below it.

Use row header for strip proxy resolutions

Use heading row for the Sequencer Flip X/Y controls

Use column header for Transform Affect Only toggles

Fix error in prior commit

Use new layout features throughout all Cycles properties

Better alignment in Experimental Preferences

Use checkbox+value for Sculpt Plane Trim & fix column headers

Option to insert blank dummy decorator for uiItemFullR

When there are multiple items in a property split row (e.g. mirror axes
in the mirror modifier) the decorator would only apply to the first
element. A dummy decorator could be inserted manually by using
`uiItemL_respect_property_split()`, but it's better to let the UI code
have an option for that, the case is common enough.

Use row headings for sculpt symmetry options

Also removed redundant columns.

Support heading in row layouts too - `uiLayout.row(heading="FOO")`

Use property split layout for sculpt symmetry options

Meant as an example of how to do this with Python. Wasn't possible
without a broken layout until the previous commit.

Fix more cases of recursive property splitting

A bit hacky, but we have to disable the `use_property_split` flag for a
row after adding the split layout to prevent it from further splitting
when adding more items. If these new items actually add multiple buttons
(vector items), these should be placed in a column like before (by
accident?). E.g. that's how the translate buttons (a vector item) is
aligned with the lock icons (another vector item).

Use column heading for Bevel tool settings