Rough support for generating .deb package 

Command for generating:
`cmake -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_BUILD_TYPE=Release .. ; make; make package`

Current lintian output:
```
E: openspades: unstripped-binary-or-object usr/games/openspades
E: openspades: binary-or-shlib-defines-rpath usr/games/openspades /usr/local/lib
E: openspades: embedded-library usr/games/openspades: libjsoncpp
E: openspades: changelog-file-missing-in-native-package
E: openspades: control-file-has-bad-permissions md5sums 0664 != 0644
E: openspades: no-copyright-file
E: openspades: extended-description-is-empty
W: openspades: non-standard-dir-perm usr/ 0775 != 0755
W: openspades: non-standard-dir-perm usr/games/ 0775 != 0755
W: openspades: non-standard-dir-perm usr/share/ 0775 != 0755
W: openspades: non-standard-dir-perm usr/share/applications/ 0775 != 0755
W: openspades: non-standard-dir-perm usr/share/doc/ 0775 != 0755
W: openspades: non-standard-dir-perm usr/share/doc/openspades/ 0775 != 0755
W: openspades: extra-license-file usr/share/doc/openspades/LICENSE
W: openspades: non-standard-dir-perm usr/share/games/ 0775 != 0755
W: openspades: non-standard-dir-perm usr/share/games/openspades/ 0775 != 0755
W: openspades: non-standard-dir-perm usr/share/icons/ 0775 != 0755
W: openspades: non-standard-dir-perm usr/share/pixmaps/ 0775 != 0755
W: openspades: binary-without-manpage usr/games/openspades
```

Currently package can't be installed because of unresolvable libsdl2-2.0.2 dependency, but it's better then nothing i guess.

Also, some improvements in installation (`make install`).