Embed compressed case data

This changeset replaces the current hex-encoded data files with plain-text files and a method for embedding a gzipped encoding of these in the binary. It is partly motivated by the woes reported in OPM/opm-core#352. This approach has the following advantages:

* The case files are now human-readable. In particular it is possible to trace changes to them in a meaningful manner.
* The repository is now within the new GitHub size limits, as the hex-encoding was five times larger than the source files.
* The resulting binary is more compact.

This is achieved with the following trade-offs:

* The build takes slightly longer time, though I think this is negligible.
* The build now is dependent on Unix-utilities such as sh, gzip, od and sed. These probably exist on all target platforms however.
* We must link a Gzip-decompressor. However,  we already depend on Boost for opm-core so we get this practically for free.