Addon updates

Summary of changes:
 - fixed several bugs in FS addon;
 - added error checks to FS addon;
 - implemented `TNodeJsLinAlg` functions for generating (sparse) vectors and (sparse) matrices, and SVD and QR decompositions;
 - started with unit tests for FS and LA addons;
 - consistent indentation in FS and LA addons;
 - other minor stylistic changes.