Fix MultiSelect filter prop

[lochstar]

Hi,

I noticed :filter="false" was not working for the MultiSelect component. I've fixed it and also updated the docs to display false as the default value.

The disabled prop also doesn't appear to be working correctly, I've prevented the select from opening when disabled.

A couple of questions regarding the component:

1. I also noticed there isn't a way to disable the "Select All" header with a prop, however it can be done via CSS. Did you want to include another prop to hide this feature?
2. Would you accept a PR for a close-on-select prop?
3. Would you accept a PR to limit the amount of options that can be selected?

Regards

[cagataycivici]

Merged manually thanks.