#103 Remove / Encapsulate boost::multi_array (removing boost #2)

[Ulf Lorenz]

Boost is a major drag when you want to compile anything, as the huge number of headers slows down the compilation considerably.

OperatorMatrix internally uses a boost::multi_array. This should either be hidden through a Pimpl-idiom, forward-declared in a portable way or replaced by a more mundane data structure. The goal is to remove the need for every user of OperatorMatrix to include boost::multi_array.

Measure the effect of this cleanup

---

• replaced data structure by a normal, flat vector
• no relevant effect on build times