Fixes includes wrt opm-parser PR-656

Several files stopped compiling due to relying on opm-parser headers
doing includes. From opm-parser PR-656
https://github.com/OPM/opm-parser/pull/656 this assumption is no longer
valid.

examples/compute_eikonal_from_files.cpp

@@ -34,6 +34,7 @@
 #include <memory>
 #include <algorithm>
 #include <iostream>
+#include <fstream>
 #include <vector>
 #include <numeric>
 #include <iterator>