Make acceptable termination status more flexible?

[wzhangw]

Right now the only acceptable termination statuses for node problems are MOI.OPTIMAL and MOI.LOCALLY_SOLVED, as coded in https://github.com/kibaekkim/BranchAndBound.jl/blob/master/src/impl-JuMP.jl#L65. In some cases it might make sense to include some other possible statuses. For example, it is very common to see MOI.SLOW_PROGRESS when Mosek is used to solve SDP problems in JuMP.

As a further step, we may even allow users to add acceptable termination status through some interface function?