Add reworked `deadline_label` implementation to Task class.
Reworked sqltablelisting textfilter functionality.

Define searchable_columns in the BaseTableSource instead
of guessing the columns on the configured helper.
Dropped `overdue_date_helper` and replaced with lambda function.
Added taskquery option `by_brain`.
Reworked _get_task_css_class helper, it uses now task objects `get_css_class` method.
Fixed css_class getter in the task byline.
Reworked `Task.get_link` use css_class getter of task, instead of passing it by.
Merge pull request #474 from 4teamwork/pg_css_classs

Rework Task css class helper
Fixed naming of query method `tasks_by_id` to `tasks_by_ids`.
Removed no longer used query adapter.
Removed dead code.
Dropped no longer used test-helper `task2sqltask` and use `get_sql_object` instead.
Moved TaskQuery utility in to tasks own query class: `get_task` -> `by_id`.
Moved TaskQuery utility in to tasks own query class: `get_task_by_path` -> `by_path`.
Moved TaskQuery utility in to tasks own query class: `get_task_by_oguid` -> `by_oguid`.
Task Query: renamed `by_id` to `by_intid`.
Moved TaskQuery utility in to tasks own query class: `get_tasks` -> `by_ids`.
QueryUtility: Dropped no longer used methods.
Dropped support for catalog listings in get_selected_items helper.

All tasklistings are Globalindex listings, therefore the support for catalog listings are needless.
QueryUtility: Dropped no longer used methods