Now using Flask-KVSession for server-side sessions

This fixes issue #7 as Flask uses client-side session cookies by
default. Session cookies are limited to 4096 bytes in size, which was
not sufficient for Figshare article details.
Removed debug code
Moved JavaScript to separate file
Removed debug code
Added entry for flask-kvsession
Servername thingies (used for testing, probably not necessary)