This removes PKG_VERSION and PKG_RELEASE from most Makefiles, as the
value was never useful for Gluon packages; instead, PKG_VERSION is set
to 1 in gluon.mk.

It also removes two other weird definitions:

- gluon-iptables-clamp-mss-to-pmtu replicating the old PKG_VERSION logic
  from gluon-core, but without the fixed PKG_BUILD_DIR to prevent
  unnessary rebuilds
- gluon-hoodselector set GLUON_VERSION=3

package/gluon-web-network/luasrc/lib/gluon/config-mode/model/admin/network.lua:122:16: (W431) shadowing upvalue f on line 19

Fixes: bab4af01 ("gluon-web-network: improve PoE GPIO name translation
handling")

- Replace string concat for i18n key with an explicit list to make the code
  compatible with i18n-scan.pl
- Improve fallback string

- CGI script and index.html are moved from gluon-web to
  gluon-config-mode-core, the script is renamed to 'config'
- gluon-web and gluon-web-model base views and i18n files are symlinked
  into the new path
- gluon-web-theme is renamed to gluon-config-mode-theme and installs
  directly into the new path
- all gluon-web-* models, controllers and views are moved into the new
  path

The 'auto' attribute still allows enabling the interface using ifup, which
is not intended when wired mesh is disabled.

Fixes #1269