fix Makefile
use luci-lib-json instead ob luci-lib-jsonc
remove obsolete sites.lua
fix and improve 005-set-site-config

In actual gluon master the site.conf is converted to site.json during build, so the created site.conf has to be stored as site.json. Additionally the conversion during build is done for the associated config files, too.
Actually the following config files are used by this programm:
- $(GLUON_SITEDIR)/site.conf -> /lib/gluon/site-select/default.json
  - the default site-config
  - is used as basis for new generated sites
- $(GLUON_SITEDIR)/extra/sites.conf -> /lib/gluon/site-select/sites.json
  - contains the individual site-config for each site
  - these changes are added to the default site
- $(GLUON_SITEDIR)/extra/groups.conf -> /lib/gluon/site-select/groups.json (if file exists)
  - with this file you can define some individual config for a group of sites
  - changes are applied to default site, before sites.json
  - set site_select.group='group_x' in sites.conf for each site, which should use a group called group_x

split ffho-config-mode-site-select in:
- ffho-config-mode-site-select (for the UI, needs ffho-site-generate)
- ffho-site-generate (for the site-generation)
- ffho-upgrade-tools (for migration-scripts)

split ffho-config-mode-geo-location in:
- ffho-config-mode-geo-location
- ffho-upgrade-tools (for migration-scripts)

DATA, BIN} macros.

Using these macros (instead of $(CP)) in the Package/.../install section
ensures correct permissions of the files installed in the image.
The two scripts ffpb-debug and ffpb-debug now get installed using
INSTALL_BIN, while the (orphaned) cron-file gets installed using
INSTALL_DATA. In both cases we ensure that the directories exist by
calling INSTALL_DIR (with parameters "/bin" and "/lib/gluon/cron"
respectively) prior to installing the files.

First of all, the ffpb-debug script is now written in lua and thus requires
a lua interpreter to be installed. But since the script makes use of some
gluon-specific lua-functions/-variables (such 'site_conf' in site_conf.lua),
we have to make ffpb-debug depend on the 'gluon-core', which in turn would
define all other dependencies.
Moreover, since ffpb-debug-live got rewritten to work with Barrier Breaker
(i.e. gluon 2014.4 and later), the already defined dependency towards the
busybox package does not suffice any longer, as we fetch interface-details
and -statistics via ubus now. As ubus outputs its data in JSON, we moreover
need the helper functions from the 'libubox' package for a convenient hand-
ling of such data in shell scripts.