Cbi settings

This commit will restructure the way that nodogsplash is handled in the luci menu's.

SEE: https://github.com/opentechinstitute/luci-commotion/pull/195
SEE: https://github.com/opentechinstitute/commotion-feed/pull/50

To Test:
1) Build and image from the following commotion-feed branch: "commotion-splash-cbi"
2) Add the following branches for makefiles to pull from:
luci-commotion-splash: cbi_settings
luci-commotion: commotion-splash-settings
3) Complete the setup wizard.
4) Enable the welcome page in "Basic --> Client Controls"
5) Confirm that the welcome page was added.
6) Go to "Advanced --> Services --> Captive Portal"
7) Perform a variety of nodogsplash configurations on this page. 
8) Confirm that the nodogsplash config file is correct
9) When nodogsplash is supposed to be on confirm that ``` ndsctl status``` affirms the correct setttings
10) when off, ```ndsctl status``` should show it as off.
11) All settings should be reflected in the splash page options