Add a ProjectMap plugin

This implements a plugin for project detection using a file that's located in ~/.waka-projectmap that determines the project name from the project's path relative to the user's home folder.

Example .waka-projectmap:

```json
{                                                 
    "/dev/projects/SomeRandomFolderName": "Top Secret Project A"
}                                                 
```

The folder path needs to have a leading slash and no trailing slash as that's how it's currently compared in the plugin.