userportal, webadmin: use json for documentation mapping files

Convert from using csv to json for documentation mapping files.

Create new HelpTagJsonServlet to serve the json files to web apps. The servlet is
configurable to allow multiple json files (so there can be a common file shared
between webadmin and userportal). All configured files are merged into one json
String at init time, and cached (to limit server calls).

This backport also includes fix found in http://gerrit.ovirt.org/#/c/24212/
and http://gerrit.ovirt.org/#/c/24207/

Change-Id: I4d6e8be143583d253943445842c2851fb52274e6
Bug-Url: https://bugzilla.redhat.com/1014859
Signed-off-by: Greg Sheremeta <gshereme@redhat.com>