tigefa4u projects Trac

* Extend the {{{IEnvironmentSetupParticipant}}} so that is also involved with upgrades.
* Factored out initialization related to attachments and templates into the {{{trac.attachment}}} and {{{trac.web.chrome}}} modules, respectively.

make sure errors in generator-based mimeviewers are caught and fall back to the next best renderer (fixes #1685)

process inline WikiFormatting in headers (fixes #608)

Allow empty values for milestone and version on ticket created. Fixes #1698.

Added a dummy HelloWorld-macro implementation to formatter.py to allow all unit tests to pass.

* Make milestone and version optional again. Closes #1698.
* Fix custom fields of type 'radio'.

Some style fixes. Should fix #1261 and #1675.

Quick fixes to notification code broken in [1831].

Refactoring of the ticket module so that the available ticket fields are collected in a central location. This should result in all modules (ticket, newticket, query, milestone) using the same set of ticket fields. Fixes #1668. Also:
* Add model classes for each of the entities used as ticket fields (component, version, priority, severity, etc)
* [wiki:TracAdmin trac-admin] now uses those model classes instead of direct SQL.
* Improved layout of the form for creating/modifying tickets.
This change is pretty big and may introduce regressions. Please test and provide feedback!