Sanity check for plugin name

[sirloon]

With source code being generated now, plugin names must be checked because they give the names for dumper and uploader classes.

• must stat with a letter
• no dash

regex: /^[A-z_][/w/d]+/ ?

[sirloon]

done in https://github.com/biothings/biothings.api/commit/c6ede427e218c931f924a33a099b8a033f99623e