Fixed a bug regarding unicode strings.

The function vitables.utils.toUnicode has been removed.
Some minor changes (typos and similar things) have been done.

A typo has been fixed and a new module added to vitables/__init__.py.
The Plugins Manager has been debugged.

The imp module has been replaced with the implib one. The whole code
has been reviewed, debugged and simplified as much as possible (at the
moment...)
The timeseries plugin has been debugged. Interpolation errors have
been fixed.

Using the configparser module instead of the old ConfigParser one had
some interpolationn problems. Those problems have raised today while
checking the code and have been debugged.
The development of a plugin for sorting the databases tree has started
:)

As requested for some users I'm developing a plugin for sorting the
databases tree. It has forced me to give some extra love to the
plugins manager.