form-field-procs.tcl

- new form-field parameter: show_raw_value
allow optionally to show the value of form-fields as raw values
- support for disabled composite fields
- new form-field class 'page':
similar to form_page, but is a simple selector
for arbitrary pages of arbitrary classes.
'page' supports as well a match-pattern for the page name.
- some refactoring of page and form_page to abstract_page
- new configuration option for form fields 'behavior':
one can now define the behavior of form fields via
form-constraints (e.g. some_field:page,....,behavor=SOMENAME)
where the behavior corresponds to a mixin class. This way
e.g. all renderings can be influenced on a per form-field
level. The behavior might be application specific.