M::M::Update: Use slash as multigraph sub-graph url separator in sql

This makes sub-graph urls generated by munin-cgi-html match the old
static html pages:

    http://host/munin/DOMAIN/HOST/diskstats_iops/sda.html
M::M::U: Add number of subgraphs as service_attr in SQL

Add a 'subgraphs' service_attr for multigraph services.
cgi/html: Display graph info in service view
cgi/html: Hide not graphed fields from legend
cgi/html: Detect and filter multigraphs from node service overview
cgi/html: Change URL ending for services with sub-graphs to '/'

This matches the original static html, which treats non-leaf services
as nodes.
cgi/html: Support multigraphs
static/zoom.js: Remove erroneous semmicolon

Commit 64dfec7 "Rename cgi-bin to munin-cgi" added an extra semicolon,
resulting in a truncated URL for the graph image.
template/head: Add closing tag for dynazoom <script> tags
cgi/html: Enable dynazoom of service graphs
cgi/html: Let HTML::Template generate __(odd|even|last)__ tags
cgi/html: Side navigation links should use R_PATH and relative paths