Enable/disable with links to executables instead of aliases

[sfertman]

I found aliases a bit unpredictable to work with. Also, shell needs restarting for (un)aliasing to take effect.
New plan:

• make a bunch of executables on install (node, npm, ...).
• enable by creating links to them in some dir on $PATH (e.g.: ~/.local/bin).
• disable by deleting those links.