Replaced #include "storm/.." with #include <storm/..>

[volkm]

Fixes #231

Might need to be adapted if #367 is merged first.

[sjunges]

Nice! Maybe we should have an automformat rule that there must be an empty line between a block of <> includes and "" includes? Either way, LGTM!

[volkm]

I added a rule in clang-format such that it should now enforce the following order:

#include "header.h"

#include <system-library1>
#include <system-library2>

#include "src/core/header1.h"
#include "src/core/header2.h"

Automatic sorting can be disabled by

// clang-format off
#include <storm/models/sparse/Pomdp.h>  // Must be included before verification.h
// clang-format on

[sjunges]

perfect!