bug fix with the initial size of the user definitions plugins

Replaced the 'generate' button on the bottom of the panel

Bug fix with SphericalQVectors (no status start defined)

viewer are no longer plugins.
Improved significantly the ergonomy of the periodictable viewer
The user can now performs several atom selection and transmutation.
Improved the atom list widget
Fixed several bugs
Added new icons

viewer
Bug fix when closing a lugin pane
Bug fix with DL_POLY converter plugin

alunched as standalone widget of used as a plugin

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

Relocated several packages

Bug fixes with user definition related widgets

Modified a bit the validate method of UserDefinition derived classes

anymore.

Bug fix that was making the sphinx-build very slow

conflicts
Refactored many GUI related module to make the main app restartable

reintroduced now