Use Lambda functions for post cmd actions

@ch3cooli 
What do you think? Despite one point (https://github.com/TortoiseGit/TortoiseGit/commit/e33f96fa789c877588b6e73e3de3045b88635f83#diff-40e225ca2b028c63d6dbfd5c89984442L2638) this could be easily reused for GitProgressList.

Is https://github.com/TortoiseGit/TortoiseGit/commit/cb27b290a5574cdf91f6e1f919023dea682b19c5#diff-4ffaa11faf02d0b88341268bb3d483a9R52 problematic with VS2012 again?

When we use much more GitProgressList & libgit2 we should find a nicer solution for retry (i.e., without closing the dialog?!).