build: introduce luci-base Merges libs/core, libs/ipkg, libs/web, libs/sys, libs/sgi-cgi, libs/sgi-uhttpd, modules/admin-core, themes/base and protcols/core into modules/base and renames luci-lib-core to luci-base.
themes/base: forgot to scale down one image
themes/base: add icons for wifi, ethernet, switch, bridge and signal