The Plugin class and discover steps were updated. Some test are deleted
because they were obsolete (discover method do not take any argument
anymore)

Here is a rewritten test suite for Regex DataHandler. This rewrite aims
at being lighter, more readable, accurate.

The previous test was testing FormatString.construct_data which is
irrelevant to this test case. Thus, I rewrote it to test what Concat
does : format a format_string to initialize FormatString with.

There were manual import through importlib, we have to replace them with LodelContext calls.
Actually the plugins module is in a dirty state....

solves #58

IMPORTANT : tests are broken. See details below

A new lodel/buildconf.py.ini file created. It will be transformed to a lodel/buildconf.py file by ./configure .
This file goal is to store build time constant (for the moment the presence of pymongo).
You have to build lodel2 before being able to run the tests.

- now runtest runs also make refresh_plugins in the test instance

Import bugfixes in settings validator. Hooks must be imported in validatore definition to avoid circular import failure

Implements both Plugin child classes handling extensions and session handling.
Modified the settings plugin preload piece of code. It is now adapted to the new plugins organisation.
Each Plugin child classes provides a confspec indicating where the plugin list is stored in configuration.

Deleted hardcoded condition that brokes standart field validation process