Move classes required for Lua runtime support into a new `luci-lua-runtime`
package. Also replace the `luci.http` and `luci.util` classes in
`luci-lib-base` with stubbed versions interacting with the ucode based
runtime environment.
Finally merge `luci-base-ucode` into the remainders of `luci-base`.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
