Fix T38706: dropdown labels in popups not updating

Caused by own recent changes to menu handling
Fix T38714: MeshPolygon.center not a Vector type
PyAPI: bpy.ops was showing 'module' in autocomplete output
Fix T38715: Setting object mode fails from command line

also run load pre/post callbacks
blender-thumbnailer.py: Fix GVFS support not working with Python 3

also update doc string.
Fix T38567: Branch smoothing on skin modifier broken

own regression when changing delete commands
MSVC: improve warnings for scons and cmake

Some int/float conversion warnings were disabled by buildsystems but
re-enabled by BLI_winstuff.h, the warnigns relate to conversions not
considered issues on other systems so better just quiet them.
MSVC: add more warnings to match OSX/Linux
Totally remove BSP from SConscript
Update the camera presets in various ways:

* Switch to using Canon sensor type instead of camera models.
There are a ton of camera models that reuse the same sensor
so it's just confusing and forever incomplete to try and cover
all models.

* Delete all redundant Canon camera models..

* Leave only the Canon camera models that are special, that is
have non regular sensor sizes.

* Fix a few errors in some Canon models.

* Capitalize a few unrelated sensor presets for consistency.

* Added presets for GoPro and iPhone.
Their distortion models and shutter isn't really supported ATM
but tracker is robust enough to give reasonable tracking and
solving results.

Presets are from Daniel Salazar and Sebastian Koenig, thanks!

Differential Revision: https://developer.blender.org/D264
BSP was still hanging around in CMake
Code cleanup: de-duplicate ndof controls for walk/fly mode
NDOF: fix helicopter fly option, revert default to trackball.

Rationale for using trackball is that it allows roll which you expect
with an ndof device.
Fix T38603: Output File node sockets were drawing the regular socket
label in addition to the actual specialized socket ui.
Camera presets changes

- Fixed typo in Canon C300 camera name
- Added preset for Nexus5
Added an option to camera preset to include/exclude focal length from the preset

Useful for cameras which have fixed focal length.
Fix T38720: Clear preview range operator missing notifier to redraw
timeline.
Added track weight to presets

Useful for cases when you need to create bunch of witness tracks.
Change default track to 15px pattern and 71px search

After recent seed improvements it makes tracking more robust
without speed loss.
Added Maya restpose_matrix support via custom properties to Collada exporter