Fix static paths in settings.py.

* STATIC_ROOT is at the same level as BASE_DIR, not in the BASE_DIR.
* STATIC_ROOT is set as an absolute path.
* Set STATICFILES_DIRS so collectstatic looks in `BASE_DIR/static`,
  not `BASE_DIR/../static`.

Fixes #11.
Merge pull request #30 from toffer/fix-static-settings

Fix static paths in settings.py.