[MDC-524] simetbox-openwrt-core: create package

[MDC-524] simetbox-openwrt-core: create package

Create a core package that is used for lac-bcop-1 functionality, as
well as for SIMETBOX setup of OpenWRT functionality (i.e. not related
to the measurement engine itself).

A lot of what is in simetbox-openwrt-base will eventually migrate to
the new simetbox-openwrt-core.