Keep SASS style scoped in .vue component

[Dalanir]

We wanted to add the possibility to override some style variables (e.g: active-color), we thus had to remove the scope attributes on style block, that prevent to overwrite a class not on purpose.

So now, we've got style in a separate file that prevents the style to be computed before we can override it in another project.

I think a better solution can be found in order to follow Vue convention 'Single File Component' , but I failed to find it.

[davinov]

While working on #515 I also noticed that some styles for vue components are not scoped, like in the MultiInputText. In that component, vue-multiselect is restyled, which has implications everywhere its used. I think that's not a good practice, we should aim to scope all styles.