Restore promises polyfill (fix #323)

Functionality was removed in 8aca77384c932f85148ad56caa892bc318358ed6
by mistake.
test: test early resolve of setItem for Blobs
fix(localStorageWrapper): fix early resolve of setItem for Blobs
Merge pull request #322 from thgreasi/lsEarlySetItemResolve

fix(localStorageWrapper): fix early resolve of setItem for Blobs