add a special kernel for eigenvalue problems #2350
add the inverse power method and nonlinear eigenvalue executioner #2350
add two objects in test #2350
two tests for the eigenvalue executioners #2350
move some codes from EigenExecutionerBase to NonlinearSystem and other improvements #2350
Refactor EigenKernel
Adding multiple EigenKernels to the warehouse
TODO: Need to address proper execution
Implementing new EigenSystem
a new working version #2350
Few corrections #2350
a test showing how to use materials for the eigen executioners #2550
Merge pull request #2791 from YaqiWang/eigen_executioner_2350

PR on eigen executioners 2350
Merge commit '72fc4ca68c298ad7aa977ce624ca06d20e23bc54'