EigenProblem

[friedmud]

We need an EigenProblem for solving a generalized eigenvalue problem (Ax=\lambda Bx).

We should reuse the kernel system for filling in A and B with the idea generally mapping to input file syntax that looks like:

[ [./A](EigenKernels]
)
    [   [../](./my_kernel]
)
  [ 
  [./B](../]
)
    [   [../](./some_kernel]
)
  [../]

Then use the computeQp*Jacobian functions to fill in the matrices.

[friedmud]

For now, we're going with @YaqiWang 's implementation as detailed in #2350