add network connection notifications

[mrose17]

supercedes #3973 (reduce to 1 commit)

Test Plan:

disconnect the network. reconnect the network. 1 second later the ledger client code will run as will the code that gets the balance.

auditor: @bridiver

[luixxiul]

Would someone please specify STR to confirm the issue has been fixed?

[bridiver]

there is a test plan above, but I think it needs a better method to verify in the release builds. @mrose17 is there something they can check in the interface? Log output is not readily available in the release builds to confirm that the code is running

[mrose17]

@bridiver - you can always get log information, it's just a matter of how you start the browser, e.g., LEDGER_LOGGING=true LEDGER_VERBOSE=true /Applications/Brave.app/Contents/MacOS/Brave

although i agree with the point that it ought to be easier to test it.

@ayumi - what do you think about a follow-on issue in which, on appConstants.APP_NETWORK_CONNECTED, we update ledgerInfo.error with a string saying "Internet inaccessible, so updates unavailable." ?

[ayumi]

@mrose17 Right now there's a message saying "error, can't retrieve data" which covers being offline I think.
Are we going to show general notification of offline status – I think maybe @bsclifton suggested it here #3973 (comment)?
If so the user would know they're offline.

[mrose17]

@ayumi - perhaps this is a non-issue, then.

certainly a general notification along the lines of what @bsclifton suggested in a post-1.0 timeframe would suffice.