Improve visualization UX

[clemsos]

Now it is very rough and there is even useless buttons and info. This should be the most appealing page to the user.

• rewrite header
• remove useless button "download as CSV"
• improve list display on the right of the network graph
• center and enlarge graph
• improve word force for better display : links should have weights
• colors : red is very bad for links
• annotations : quantity of words

[clemsos]

Merge #28 fix most of the problems here

[clemsos]

Looks better already !