Allow multiple execute_on options
MooseEnum => std::vector<MooseEnum>
closes #3446
Switch user object to timestep_begin
Actually run timestepSetup at the beginning of the timestep for all UOs, not just the timestep or timestep_begin UOs - the side effect is that we run it once instead of several times.
Fixing up Modules
Merge pull request #3463 from permcody/shared_multiple_execute

Shared multiple execute
Merge commit '968823bc749711141d9fd663835ee73a3683b3b7'