* src/TextClass{cpp,h}:
- implement Requires tag for class and InsetLayout.
* src/Layout.{cpp,h}:
- implement Requires tag for layouts.
- increase layouts format to 6.
* src/Paragraph.cpp:
- request required features for paragraph layouts.
* src/LaTeXFeatures.cpp:
- add some packages needed by modules.
- remove Preamble method for InsetLayout. This is now done
in InsetFlex::validate.
* src/BufferParams.cpp (validate):
- request required features for the class.
* src/insets/InsetLayout.h:
- new member "requires".
* src/insets/InsetFlex.{cpp,h}:
- implement validate method and request required features and preamble snippets.
* lib/layouts/*.{layout,module,inc}:
- increase layouts format to 6.
- use Requires tags in some modules (more can be done later).
* lib/doc/Customization.lyx:
- document Requires tag.
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@22414 a592a061-630c-0410-9148-cb99ea01b6c8
