Improvement (#449)

Add new settings for panels size
Add screening for extensions
Add extension scan and selector
Allows to move extra content panels individualy
Allow to move panels by drag and drop in dash board
Allow to store extensions in extensions sub directory or root but not both
Allow to store language packs in languages sub directory or root but not both
Allow to store themes in themes sub directory or root but not both
Refactoring of the test server for esier maintainability
Improve packing process to decrease final package
Remove some icons that seems not useful in webui context to decrease final package
Save in preferences.json only differences from default values
Minify preferences.json to decrease file size
Update severals styles for UI consistency
Update all translations pack
Add several tools for easier language update including tools to detect missing translations/ automate translations / update missing translations
Remove smoothie package to use a stripped version to decrease final package size
Update browser list and hash

Author: luc-github