use green color for graph nodes

- also use stylesheet and classes instead of directly
  injected css.
PostgreSQL example database config.
Add installation script
change color of edge dependent on link-type.
Merge branch 'master' of github.com:ontohub/ontohub
Moved Daniels install script and changed some lines.
enhance the styling of graphs and related infos.
fix path after node selection issue

When selecting a path(edge) after a node(node)
the node stayed visually selected.
add functions to add/remove classes in svg.
show an edge as selected when it is selected.
improve highlighting of nodes when hovering.
improve drawing of edge arrowhead.
highlight nodes when hovering on pertaining edge.
display graph related notifications

If a graph has no edges we do not display it at all
and show es specific notification. As long
as we load the graph we show a graph loading
notification.
add modes to ontology-graph display

Add support for import and normal mode supported

- import: Show only links with kind: import_or_view
- normal: Show all links.
show symbols as links in graph node view.
Better installation script plus script to start basic development servives.
Added database configuration to installation script.
highlight active mode selection for graphs

- also replace buttons (with nested links) with
  links.
use utf-8 arrows instead of ascii-style arrows.