Add `FLUENT_PAGES_DEFAULT_IN_NAVIGATION` setting

Allows larger sites to set the default "Show in navigation" choice.
(cherry picked from commit d2557485656d2f3f8981be9db367e4387bd0a5d7)

Conflicts:
	CHANGES.rst
	fluent_pages/appsettings.py
Widen modification_date column, to support other languages.

E.g. Italian output: "mercoledì 11 settembre 2013 00:16:34"
(cherry picked from commit a9652383c4715282ebee353a2a87a50b17331d45)

Conflicts:
	fluent_pages/static/fluent_pages/admin/pagetree.css
Also add url_pattern_types() to the manager class.

(cherry picked from commit 38b25d76f95b81bc95b9206921ab5445ba6e800d)
Fix using `{% appurl %}` for modules with multiple results.

(cherry picked from commit 556e5f98a17b11dd50de34927856c06366ec22ee)
Add notice about _current_fluent_page.

Turns out django-fluent-blogs code actually reads this variable too.
(cherry picked from commit de6a82ef010e943e54150fa0e3493a350939b32d)
Add traceback to runtests.py

(cherry picked from commit 8707de18b5176fe94ec573ccbf7264014148c26e)
admin: warn when fluent_layouts.ct_id is not defined in the template.

(cherry picked from commit ab28197a23bbf350df5bde5118e1b12d437d1220)
Update version and changelog to 0.8.6
Merge branch 'v0.8.x'

Dropped all changes except CHANGELOG,
as all other changes were cherry-picked.

Conflicts:
	fluent_pages/__init__.py
	fluent_pages/appsettings.py
	fluent_pages/models/db.py
	fluent_pages/models/managers.py
	fluent_pages/static/fluent_pages/admin/pagetree.css