Ftw-builder

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- Add more default builders:

- a "zcml" builder for creating ZCML files
- a "python package" builder for creating python package on the file system
- a "namespace package" builder, used internally by the "python package" builder
- a "subpackage" builder for extending a python package with nested packages
- a "genericsetup profile" builder
- a "plone upgrade step" builder for building Generic Setup upgrade steps

[jone]

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- File builder: fix default filename encoding for AT.
This was a regression in 1.5.0, where filenames were changed to unicode
because of the consolidation of Archetypes and Dexterity builders.
[jone]

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- Fix NamedBlobFile import issue for Plone <= 4.2 where blobs are optional.
[jone]

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- Restore Plone 4.1 compatibility by making any DX imports conditional.
[lgraf]

- Plone 5 support: default content builders are switched to the dexterity implementation
by default for Plone >= 5.
The builder classes were moved from ``archetypes`` module to ``content`` module.
[jone]

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- Implement collection builder.
[jone]

- Fixed default value setter for different "owners" field.
[phgross]

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- DxBuilder: Fix encoding problem when filling default value for "owners" field.
[jone]