Blender Git Loki

Application Templates: make templates more prominent in the UI.

The goal here is to make app templates usable for default templates
that we can ship with Blender. These only have a custom startup.blend
currently and so are quite limited compared to app templates that fully
customize Blender.

But still it seems like the same kind of concept where we should be
sharing the code and UI. It is useful to be able to save a startup.blend
per template, and I can imagine some scripting being useful in the future
as well.

Changes made:

* File > New and Ctrl+N now list the templates, replacing a separate
Application Templates menu that was not as easy to discover.
* File menu now shows name of active template above Save Startup File
and Load Factory Settings to indicate these are saved/loaded per
template.
* The "Default" template was renamed to "General".
* Workspaces can now be added from any of the template startup.blend
files when clicking the (+) button in the topbar.

* User preferences are now fully shared between app templates, unless
the template includes a custom userpref.blend. I think this will be
useful in general, not all app templates need their own keymaps for
example.
* Previously Save User Preferences would save the current app template
and then Blender would start using that template by default. I've
disabled this, to me it seems it was unintentional, or at least not
clear at all that saving user preferences also makes the current

Differential Revision: https://developer.blender.org/D3690