Improve Script-server behaviour, when web libraries are missing

[bugy]

Currently web libraries should be downloaded separately from the repository (using tools/init.py script). If a user forgets to do it, then the UI would look broken.

There should be a message on UI about problems with loading the libraries, instead of showing the broken interface.
Also Script-server can validate the libraries on startup and WARN user if they are missing

[bugy]

Validation on web page is not possible.
I added validation on server startup.
Should be tested in win

[bugy]

Works fine on windows as well