web-ui: fixed problems with spaces in file paths

The problem occured when either Lattice Builder or Python were installed under
a directory with spaces in its name.
improved the manual
web inteface → web application

Web Application is the appropriate usage, according to Wikipedia.
updated README

Easier to find download links.
New Quick Start Guide.
Removed some redundancy.
web-ui: clarified the interface
web-ui: warning if no weights
patched python-jsonrpc for Python 3
relax the requirement on Python >= 2.7

Was Python=2.7, now is Python>=2.7.