more robust settings in pre-merge phase

when we haven't migrated yet, there is no settings table.
this doesn't hinder plugins to read/write settings (when
initializing the app).

solution: ignore setting-writes (but give a warning) and
answer an empty hash on setting-read when there is no
setting-table.

fixes #1830
Removes updated_at/on columns from model journals
Ignores updated_on/at fields
Adapts diff view to missing 'update_on' attribute
when there is not settings table return nil when asked for a setting
Merge pull request #372 from opf/bug/message_journals_table_requires_updated_on

[BUG] Message journals table requires updated on
Moves issues helper tests to user mailer specs
Adds changelog entry
Moves PE validation to WP
Also passed project explicitely to hook
Allows inter-project work package hierarchies

[skip ci]
Merge pull request #395 from opf/feature/rails3_add_project_param_to_hook

Also passed project explicitely to hook
Adds changelog entry

[skip ci]
Merge pull request #386 from opf/feature/rails3_let_settings_survive_wo_table

more robust settings in pre-merge phase
Merge pull request #382 from opf/feature/migrate_helper_tests_to_wp_specs

[FEATURE] Migrate helper tests to work package specs
allows for all work packages to be shown when only one project is queried
removes planning_element api list action - never used
updates changelog
Merge pull request #394 from opf/feature/move_pe_validation_to_wp

[FEATURE] Move planning element validation to work package
travis thinks it's ok, changes don't break anything, fine for me (but see the comment on rights with parent-workpackages)
Merge pull request #396 from opf/fix/timelines_issues_without_reporting

Fix/timelines issues without reporting
All tests and especially the new show.feature run through both locally and on jenkins(only travis is a little slow today), so good to go.