Avoid commiting configs inbetween to decrease number of flash writes.

Fixes #714.

Should be redundant after 0bd0df6f

gluon-announced and gluon-announce are merged to gluon-respondd.

introduce function to recurse down to the lowest layer-2 interface
corresponding to a given interface.
also re-introduce some of the previously removed input validation plus
some more to protect against glob and path based exploits.

The statistics data is now cached for 5s, no need to send an event every
second. The new interval is 3s, which is coprime with the cache timeout.

By not executing all scripts from gluon.announce themselves, both should
be considerably faster and lighter on RAM usage.

Now that the status page api has been rewritten in C CPU load and memory
usage is much lower. Also, nodes with both ibss and 11s mesh and dual
band wifi may require up to 9 connections for a single client, thus the
previous limit of 12 seemed a little low.

This will make it easier to replace the API with C programs.