Add a separate plugin-list.json file for storing which plugins are
available and the path to pass to require in order to load it. This
allows plugins to be published and installed as npm packages. And also
replaces the old method of installing plugins by putting them in the
plugins folder.
Add the statuses unknown and unassigned for when the status has not yet
been set by a slave and replace the initialized status with starting,
creating_save and exporting_data.
Replace usage of .constructor.name with a separate property to avoid
issue with JavaScript terser mangling the class name during minification
for the web build.
Split up codebase into the packages @clsterio/lib, @clusterio/master,
@clusterio/slave, and @clusterio/ctl using lerna to manage them. This
will allow deployment to use only the parts needed reducing install
size, and better separate the code into shared library, master, slave
and control.