feat(sortable): update local variable with active options
feat(sortable): add workaround for horizontal lists
test(sortable): add tests for horizontal lists workaround
docs(README): add section about floating workaround & example
fix(sortable): clear ui.item.sortable properties after drag stop
test(sortable): add tests for ui.item.sortable proper destruction
refactor(sortable): replace for-in-hasOwnProperty with angular.forEach

This also brings code coverage back to 100%.
feat(sortable): add extra properties to ui.item.sortable
tests(sortable): add tests for the properties of ui.item.sortable