[Startup] Re-do network config scripts

Hopefully this will cure the issues of losing static IP on wlan0 when
the wireless reconnects as well as some reported cases of loss of
network connectivity when not using wireless.
[Networking] Disable power management on wlan0
[Networking] Don't touch interfaces file if not configured via UI

If the user has not configured eth0 or wlan0 via the UI, don't touch
/etc/network/interfaces at boot other than to copy from
/etc/network/interfaces.default.  This allows users to customize
/etc/network/interfaces.default if they choose to to enable bridging,
etc..
[Networking] Single-quote SSID and PSK to allow special chars

In the interfaces.wlan0 config file, single-quote the PSK and SSID
values so that special characters like $ can be used.  Previously,
when sourcing the config file to setup the network, the $ would be
interpretted by bash as the start of a variable name and the config
generated would be broken.  Single-quoting these strings forces
bash to ignore the $ and other special characters in the PSK.
[Networking] Allow connection to open wireless with blank PSK
Merge branch 'networking'