Let's have a first step of components refactoring. To be included at least (in a continuous integration way please):

• The upgrade of litHTML to litElement
• Replacing the SolidTemplateElement rendering mechanism by LitElement too
• The integration of the conditional-display feature into the framework
• Some improvements for loading time:
  • We may want to separate solid-map and calendar and a few others which depends on external libraries to their own repositories, to avoid useless loading time linked to the import of those librairies
  • Exploring the question of shadowDom for good ?