refactor list: remove useless variables

Use global size variables instead of specific variables.
feat date picker: add date picker component
chore demo: add date picker link in sidebar
chore demo: moment dependency in installation doc
feat date picker: add label attribute

Add label attribute to specify label on text field.
fix date picker: use moment local locale

Define moment local locale instead of moment global locale.
Merge pull request #61 from lumapps/feat/date-picker

feat date picker: add date picker component