Project filtering is broken on roadmap page when grouping is enabled

[Cinc-th]

With [14992] and [14993] the roadmap page handling was rewritten. #12031 aims to link milestones and versions to one or more projects. Currently milestomes and versions without any link to a project are dropped from display when grouping is enabled. This may or may not be because of the recent changes.

Problem is that several SMP plugins add data in post_process_request() to the data dict given to the template in the end. This data may or may not have been filtered inside every single plugin according to the filter settings solely handled by SmpRoadmapProjectFilter.

Things are even worse because the execution order of post_process_request() is arbitrary so it's not ensured the filter plugin runs last (at least if you don't want to specify order in request_filters).

To fix the problem I intend to do the following:

1. Create a new interface IPrepareRoadmapData
2. Plugins may implement the interface to add/remove data from the data dictionary instead of using post_process_request()
3. Use OrderedExtensionOption to specify a distinct order of execution
4. Create a SmpRoadmapModule plugin to orchestrate everything by calling all the extensions in the given order during processing of post_process_request().

[Cinc-th]

In 14999:

• New interface to provide data for the roadmap page.
• No more filtering by project in SmpVersionProject. This plugin only adds its data now.
• Component SmpRoadmapProjectFilter rewritten. It does all the filtering for the roadmap in one place now.
• SmpRoadmapModule created for proper calling of data gathering functions in other components.

Fixes #12556

Refs #12031 esp. comment:9

[Cinc-th]

In 15000:

File api.py missing in [14999] added.

Fixes #12556

Refs #12031 esp. comment:9

[Cinc-th]

In 15001:

Add project selection control only to roadmap preferences. LEave timeline prefs alone.

Refs #12556

[Ryan J Ollos]

In 15390:

0.5.1dev: Fix incorrect import from [15000]

Refs #12556, #12031.