cgi/html: Do not lowercase image URLs

Image URLs contain group and node names, which may have uppercase
characters. Lowercasing the URLs results in images not found,
breaking the overview pages.
cgi/html: Sort groups in navigation bar by name
cgi/html: Sort categories in navigation bar by name
cgi/html: Sort groups and nodes by name in overview
cgi/html: Get distinct categories for node views

Original code resulted in duplicate categories
cgi/html: Fix group overview listings

Original code resulted in listings from the wrong group.
cgi/html: Generate correct navigation path with links
cgi/html: Sort categories for each node in group overview
cgi/html: Generate correct relative links for sub-groups and sub-nodes
cgi/html: Do not lowercase category names in URLs

Ideally this should be done in munin-update, when the data
is written out.
cgi/html: Add node service categories to navigation bar
cgi/html: Note the last element of navigation path

This is used by the footer navigation template.
cgi/html: show name on navigation bar before categories/comparisons
cgi/html: Add same level groups for bottom navigation bar on group views
cgi/html: Fix top navigation path and links for service views
cgi/html: Add same category graphs for bottom navigation bar on service views
cgi/html: Add same level groups for bottom navigation bar for node views
cgi/html: Change node URL pattern to NODE/
cgi/html: Add trailing slash to group URLs
cgi/html: Generate relative URLs for services