Deleted hardcoded condition that brokes standart field validation process

- Add an update feature to create_instance.sh script
- Updated webui plugin load instruction (running loader.start() in run)
- Updated the way EmCmponents handles EmGroup
- Updated the way EmFields handles EmClass
- Updated xmlfile translator according to EmComponent modification

- Changed the way of instanciating results object in get (using __new__ )

Now an instance is created, tests are copied in it and the run

The first ones will be the functions used for the setup and teardown of the datasource based tests

- The LeUpdateQuery implementation is broken or at least have huge performance issue
- Moved LeObject exceptions and LeQuery exceptions in lodel.leapi.exceptions

- Now returning automatic common field classname in fields method

Adding a field to all non abstract classes to store in DB the name of corresponding LeObject subclass

- now datasources are declared with two conf keys : read_only and identifier
- the old datasources plugin hook is now declared in lodel/plugin/core_hooks.py. This file is imported after lodel/plugin/hooks.py in the loader.py

- Added missing allowed_classes options to some references in em_test

- Modified again the em_test to fit with testing purpose
- First test on multi datasource query written
- debugging of query.py

- adding an EmClass to make a double link between indexes and texts
- adding subqueries infos to dump_infos method of LeFilteredQuery

- defining a new datasource named dummy2 in both tests conf and install/conf.d
- adding two class using the new datasource in em_test.py
 - index : abtract class representing indexes (two fields, name & content)
 - indextheme : thematic index, inheriting from index but with one more field "theme"

- The set_query_filter() method handles subquery creation
- The run isn't written yet...

Adding tests for the Plugin class