feat text-fields: fixed label and valid input state
chore demo: fixed label and valid input state examples
feat text-fields: dynamic value management for fixed label and valid state

Fixed label and valid input state parameters can now be set to true of
false.
chore demo : demo updated with dynamic value

Text fields demo updated with dynamic management for is-valid parameter
and fixed-label parameter.
feat text-fields: add default values for parameters

The configuration's parameters of the directives needed a value `true` to be active.
By adding a default value, if the parameters is set to no value (for example :
`is-valid` instead of `is-valid="VALUE"`) the default value is true.
Merge pull request #13 from lumapps/feat/text-fields

feat text-fields: fixed label and valid input state