Reintroduce an aq_inner into the getPhysicalPath code to fix test failures in CMF's discussion items

Optimized the `OFS.Traversable.getPhysicalPath` method to avoid excessive amounts of method calls. Thx to Nikolay Kim from Enfold

Removed the `App.version_txt.getZopeVersion` API, you can use ``pkg_resources.get_distribution('Zope2').version`` instead. Zope2's own code only calls the `version_txt` function returning a string.

On the application object, removed `PrincipiaTime` in favor of `ZopeTime` and `PrincipiaRedirect` in favor of `Redirect` or `ZopeRedirect`.

Removed `mime-types` option from `zope.conf`. You can use the `add_files` API from `zope.contenttype` instead.

Removed ZMI controls for restarting the process, these no longer apply when managed as a WSGI application.

Removed `bobobase_modification_time` from `Persistence.Persistent`, you can use `DateTime(object._p_mtime)` instead.

Removed `Products.ZReST` and the `reStructuredText` wrapper, you can use `docutils` directly to gain `reST` support.

Removed special code to create user folders and page templates while creating new `OFS.Folder` instances.

During startup open a connection to every configured database, to ensure all of them can indeed be accessed. This avoids surprises during runtime when traversal to some database mountpoint could fail as the underlying storage cannot be opened at all.

Explicitly close all databases on shutdown, which ensures `Data.fs.index` gets written to the file system.