Blender Git Loki

Fluid: Added display support for grid lines

Add texture transform options, Blender version comment.

Two texture transform options, out of several, are supported now:
- Translation (origin offset) (syntax: "-o u v w")
- Scale (syntax: "-s u v w")

For Normal Map textures, Strength (bump multiplier) (syntax: "-bm s")
is also added.

I had to temporarily replace `nodeFindSocket` with its own
implementation to be able to build, since it doesn't accept
`const bNode*` which we're using everywhere.

I proposed a simple fix: D8142 for that. If and when it gets committed,
I'll remove the duplicate code.

Blender version string is also added in the MTL file.

Test file: {F8647881}

Custom Menu: add submenu item

LANPR: GP Lineart modifier file r/w now working.

LANPR: GP modifier basic UI complete.

Move code to namespace blender; clang-format

Merge branch 'master' into soc-2020-io-performance

Add support for exporting Material Library file

**Why not reuse the `write_mtl` in `export_obj.py` ?**
Because there are no benefits except saving some time now, only to later
waste it in debugging or extending it.
Having it in C++ provides easy extensibility when we need to
add more nodes' support without having to modify node_utils.py, which
itself is a hardcoded wrapper for BSDF and normal map shader nodes.

Quick Summary:
If export_params->export_materials is true, we create an empty MTL file
with the same name (not extension, of course) in the same directory.
`frame_writer` writes its name (with extension) to the OBJ file, to
reference it, as per format specs.

MTLWriter class is added in the new files. It uses NodeTreeRef committed
recently in rBe1cc9aa7f281 for a faster way to find two linked sockets.

`frame_writer` instantiates an MTLWriter for an object which then
*appends* that object's material to the previously created MTL file.

LANPR: Modifier properties added.

GPencil: Fix selection

Merge branch 'soc-2020-greasepencil-curve' of git.blender.org:blender into soc-2020-greasepencil-curve

LANPR: Main panel should also show in Workbench.

Fluid: Minor refactoring change in workbench volume fragment shader

Using in-built functions instead of conditional operator

LANPR: Added back chaining threshold values.

LANPR: Object LANPR panel name change to Lineart.

LANPR: UI name fixes.

Refactor: LANPR file names changed to lineart.

Refactor: All struct names changed to Lineart

Refactor: DNA names and python references for LANPR.

Refactor: Rename LANPR to LineArt in DNA and compiler options