bug: featuresteps: custom field set,wp field check
timelines: custom field filters.

for now only for list and boolean custom fields.
intendation changed.
pass timelines_id for local custom fields filter.
integrative timelines custom field filter tests.

also adds these steps:
- the custom field <name> is enabled for the project <name>
- when i filter for work packages with the boolean custom field <name> set to <value>
- when i filter for work packages with the list custom field <name> set to <value>
Merge remote-tracking branch 'origin/dev' into feature/timelines_filter_custom_fields_3701
changelog.
use only custom fields for this project.
fix tests. user needs view work package permission.
Merge remote-tracking branch 'origin/dev' into feature/timelines_filter_custom_fields_3701

Conflicts:
	doc/CHANGELOG.md
add custom field values to api.
display custom fields in timeline.
api test.
use project-specific custom field api.
integrative tests for display.
Fixes filter for (none) in custom fields.

The id -1 and the empty string both need to be added as values in the
(none)-case, since (none) has to both match work packages with custom
fields with an empty value and work packages with no custom field.
Merge branch 'feature/timelines_filter_custom_fields_3701' into feature/timelines_custom_fields_display_3884
Fixes specs.

Adds empty custom values array to the generated structs, as those are
now appended on the server, even when there are no custom fields. This
also fixes minor whitespace issues.
Fixes a bug w/ (none) combined with another selection.

Of course, (none) can be selected in a list of several other options, in
which case we need the empty string fix, too.
Merge branch 'feature/timelines_filter_custom_fields_3701' into feature/timelines_custom_fields_display_3884