Adds a scratchpad plugin, which allows you to keep "scratches" of code/text
to experiment or quickly run something without the need for a project.
The plugin adds a new tool-view, which will maintain a list of your scratches
as well as allowing you to compile and run them.
The scratches live in the directory `scratches` in the data directory and
are regular documents so we get all the editing convenience of code-completion
I've had some trouble with having a portable way to run the scratches as well
some minor inconveniences I've marked as TODO in the code, so this is a WIP