Mode switching made this data invalid

Reduce reallocations by using lists instead of tuples.  This yields massive performance improvements when exporting large files.  Thanks to Rafał Brzeżański for pointing this out.

Note that it will export all sampled values - even for actually non-animated channels,
not really possible to avoid that without a hell lot more of code, and this rea is
convoluted enough right now.

Based on investigation by Detlef Jankowiak-Evers (@DeJev) and patch by Gottfried Hofmann (@gottfried), thanks.

Differential Revision: https://developer.blender.org/D1807

This can fail in some cases (batch converting for example).

By default, Blender uses a 'Null' one (rouglhly equivalent to our Empty),
but now user can also choose a 'Root' or even plain "LimbNode".

This seems to be necessary to hack around some Unity bug (see T47325).

WARNING: the 'LimbNode' option *does not* import back correctly in Blender.
Use it in pure export-only cases.

io_curve_svg.import_svg.SVGParseFloat() may parse a float containing scientific
notation without an exponent sign. For example, 1e3 is a legal float value
according to the <number> syntax:

  https://www.w3.org/TR/SVG11/types.html#DataTypeNumber

Example SVG file:

  https://upload.wikimedia.org/wikipedia/commons/2/2f/Google_2015_logo.svg

Patch by Zac Mullett (aka zmullett), thanks!

Reviewers: sergey

Projects: #addons

Differential Revision: https://developer.blender.org/D1755

Always use utf8 encoding, with error escaping

Not sure why this used to work. The old code used the bmesh faceseq
delete, which kills only the faces. This fix uses the utility
bmesh.ops.delete() with an arg that will maybe kill edges and verts too.
Also made code select all the new polys. This is not ideal (ideal would
be to select only the inner ones), but making the ideal change requires
more work.

Currently only expose packing functionality for packing
a file and all its deps into a ZIP (shared code with the cloud).
Can run directly or from the command line (without blender) via `blendfile_pack`.

Also adds subprocess_helper module which we may want to re-use elsewhere,
allowing to run external processes that don't lock blender and can be cancelled by pressing Esc.

Missed this in recent bytes -> string conversion

Invalid triangles were being detected as faces that looped back on themselves and had their edges dissolved.

Now ignore invalid triangles entirely since they will never end up as faces in Blender.

Differential Revision: https://developer.blender.org/D1740

Only effective for languages for which we have some translated manual of course
(Russian, German, French, Chinese).

Patch by @Blendify, with some final tweaks (mostly handling 'DEFAULT' language) by @mont29.

Reviewers: mont29

Differential Revision: https://developer.blender.org/D1737

Workaround for a bug in Python3.5,
however bytes on win32 are deprecated so better not use them for file access at all.

Reported by @yoshi, thanks!

Push SVG tag rectangle before calculating the matrix.
This way scale will use proper SVG width and height.

Missing import of Vector...

Blender was sharing UV's for all vertices,
while this is correct it was causing issues for Maya, 3ds Max & Unfold3D.

also quiet 'description' warnings.

Reorganize the UI into categories and renamed some settings, clean up and document the code and add new feautures, main options and plus options (e.g. adaptive curve resolution, curve type, radius settings and multi-link generation).