Turn on/off language downloads on cellular network

[pavelz]

Reintroduced from Pivotal Tracker iceboxed feature
​https://www.pivotaltracker.com/story/show/98111836

This functionality should be part of the Adblock Plus settings.

• Settings Adblock Plus: ​http://invis.io/JN3HLGS6H

There should be a new category called: "FILTERLIST UPDATES" with one item called "Use Cellular Network". The visual behavior should work like the on/off switch at "Adblock Plus".

The default behavior (opt-in or opt-out and potential notifications to users) needs to be discussed in the meeting (21.07.2015)

• should be downloaded for the first time
• show warning even for downloading languages

The wording for the description is now:
Below Use Cellular Network: "The Ad blocking and More blocking options are based on filter lists. These files include rules, which tell Adblock Browser what to block."

[pavelz]

DESIGN GIVEN
The design is outdated but the place is roughly the same. There isn't any design to talk about - add a single iOS-default switchbox. On our side, there isn't any much implementation either. We already have an event source of the network state, so when the switch says "off on cellular", we would call some function in the (already existing) api.js whenever the cellular state flips. The rest, however is an effort to be done on the extension side.

[pavelz]

Effort assessment:

Eyeo 80% : provide flagging functions in api.js to be called by Salsita. Conditionalize the filterlist download activation to be deferrable upon cellular flag.

Salsita 20% : add the on/off switch in question. Call the provided api.js functions on switch change and on connectivity change.