collection.Base: add protected for the map

did another dive into the code (was too long ago).

while map should be protected, items can get used directly:

    t.it('Create collection', t => {
        collection = Neo.create(Collection, {
            keyProperty: 'githubId',
            items: [
                {country: 'Germany',  firstname: 'Tobias', githubId: 'tobiu',         lastname: 'Uhlig'},
                {country: 'Germany',  firstname: 'Tobias', githubId: 'tobiu2',        lastname: 'Uhlig2'},
                {country: 'USA',      firstname: 'Rich',   githubId: 'rwaters',       lastname: 'Waters'},
                {country: 'Germany',  firstname: 'Nils',   githubId: 'mrsunshine',    lastname: 'Dehl'},
                {country: 'USA',      firstname: 'Gerard', githubId: 'camtnbikerrwc', lastname: 'Horan'},
                {country: 'Slovakia', firstname: 'Jozef',  githubId: 'jsakalos',      lastname: 'Sakalos'}
            ],
            sorters: [
                {direction: 'ASC',  property: 'firstname'},
                {direction: 'DESC', property: 'lastname'}
            ]
        });

    t.isStrict(collection.getCount(), 6, 'Collection has 6 items');
    t.isStrict(collection.map.size, 6, 'map has 6 items');
});

this changes for a data.Store => here we need data to convert input items into records.