Made GeoPHP accessible to the regular Neatline code.

* Loaded it in plugin.php, and
* Moved it to $NL_DIR/lib.
Read coverage data from features if they're available.

* Added tests for importing NeatlineFeatures.
* Don't import on save if the record already has coverage data.
Merge branch 'feature/feature-import' into develop.

Fixes #242.
Merge remote-tracking branch 'origin/develop' into develop