Adding new module which should be built as a separate library

This involves a few additional steps comparing with adding a single source file.

1. Create a new directory in src/lab.

2. Put all related sources there or in src/lab/common (if you think that they are generic enough and may be reused by other modules).

3. Define module-name.build.js and public-api.js files in your new directory (described below).

4. Add build routines to the Makefile:

   4.1. Define a new target, for example:

    server/public/lab/lab.module-name.js: \
        $(NEW_MODULE_SRC_FILES) \
        $(COMMON_SRC_FILES)
        $(R_OPTIMIZER) -o src/lab/module-name/module-name.build.js
   

   4.2. List this target in LAB_JS_FILES Makefile variable containing the list of all Lab JavaScript modules to be generated.