Make data folder configurable
Instead of hardcoding paths in the senpy file, allow the use of a DATA_FOLDER / SENPY_DATA variable, like in shelf plugins.
There are two (non exclusive) alternatives to integrate this feature in the plugin definition:
- Prepend SENPY_DATA to relative paths
- Use the variable name in the path
The second one is explicit, whereas the first one makes changing paths relative to the CWD to SENPY_DATA seamless.