Print in Storm library

[volkm]

We use the macros STORM_LOG_X for most of the output in the Storm library. There is also STORM_PRINT and STORM_PRINT_AND_LOG which always write to cout.
In my view, all output in the Storm libraries should use STORM_LOG_X such that we can set the log level from the outside. In particular, it should be possible to use e.g. stormpy without seeing any Storm output. When using STORM_PRINT this is not guaranteed because it always prints to cout. Therefore, STORM_PRINT should in my view only be used for the storm-cli parts.

[sjunges]

Duplicate of #829 (which i moved from issues to discussion).