[MINOR] add "description", "node" and show-node"/"show-desc", remove "node-name", v2

[MINOR] add "description", "node" and show-node"/"show-desc", remove "node-name", v2

This patch implements "description" (proxy and global) and "node" (global)
options, removes "node-name" and adds "show-node" & "show-desc" options
for "stats". It also changes the way the header lines (with proxy name) and
the statistics are displayed, so stats no longer look so clumsy with very
long names.

Instead of "node-name" it is possible to use show-node/show-desc with
an optional parameter that overrides a default node/description.

backend cust-0045
        # report specific values for this customer
        stats show-node Europe
        stats show-desc Master node for Europe, Asia, Africa