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

Specify conffiles for our packages, so they aren't overwritten during
opkg updates. While this only matters during development, it is
unintended to have different behaviour for opkg update and full firmware
updates.

This commit changes the behavior for the wan-dnsmasq to read the
interfaces to update the DNS servers on from flag-files.

This way, external custom packages which add a custom VPN WAN interface
can update the DNS server gluon is using for WAN resolving.

[Matthias Schiffer: fix up start/stop order and file permissions]

Nothing outside the config mode depends on luci-base anymore.

We also make use of the boolean support of simple-uci to make scripts
clearer.

Fixes #886

Fixes #854

Using service_start requires exporting of environment variables.

Fixes #397

This avoids poking dnsmasq every time a DHCP lease is obtained or a router
advertisement received.

This package provides a secondary dnsmasq instance on port 54 which resolves
everything over the WAN interface.