small refactoring of the save job template command line option
removed unused imports
removed white spaces

The MDANSE database is now append instead of prended to the MMTK
database search path
Removed unused method

create the mmtk + MDANSE dbs corresponding entries

Bug fix with Preferences

Improved the ClassRegistry import mechanism (avoid conflict with distro
module with the same name)
Improved the performance of the molecular viewer
Removed unused import
Bug fix in QVectors widgets

Bug fix that was making the sphinx-build very slow

Many bug fixes related to ud

Modified the Singleton class to get rid of module import path problem

Refactored the mdanse_gui script

Moved the converters to a specific menu
Reintroduced the __setitem__ for the ElementsDatabase
Reintroduced and refactored the PreferencesSettingsDialog
Refactored the PeriodicTablePlugin
Added new icons
Refactored the Icon class

Splitted the Plotter plugin in several modules

Added related MMTK manipulation at MDANSE __init__.py

reintroduced now