Added missing action sheet to be able to choose a twitter account when there are multiple configured on device.
Fixed action sheet cancelation.
Merge pull request #1 from inaka/pablo.AddingMissingActionSheet

Pablo.adding missing action sheet
Moved UIActionSheet+Blocks files to Classes folder so project compiles.
Merge pull request #2 from inaka/pablo.FixingMissingFiles

Moved UIActionSheet+Blocks files to Classes folder so project compiles.
Merge pull request #1 from inaka/master

Added missing action sheet to choose between multiple twitter accounts