To support field properties with only active cells the Box class has been
extended to give a set of active indices for a box. In addition the BoxManager
has been refactored:
- Use std::unique_ptr<Box> to enable "has no box" situation.
- Removed several unused getXXX() methods.
And the begin() and end() iterators have been removed from the Box class.
this is just the result of
```
find -iname "*.[ch]pp" | xargs sed -i "s/ *$//"
find opm/parser/share/keywords -type f | xargs sed -i "s/ *$//"
```
so if it causes conflicts with other patches, the others should get
priority. The rationale behind this patch is that some people tell
their editor to remove white space which leads to larger than
necessary patches...
