Only subscribe on connect/reconnect, remove refresh interval

[who-biz]

• Previously, epic-wallet was unsubscribing, and re-subscribing every time a challenge was received from epicbox over WS
• This was unnecessary, and subscription only needs to happen once per connection (provided connection remains alive)
• This commit moves initial subscription from a challenge response, to central Subscribe function

These changes have been extensively tested by EpicBox Server chat testers, and plays nicely with https://github.com/fastepic/epicboxnodejs.

[who-biz]

Will likely be adding to these changes to remove most of the refresh_interval code, as it's not needed in most places any longer... But, wanted to get these in so that epicbox initiatives can move forward.

[who-biz]

Just added a commit in 8173171 that removes the unnecessary refresh interval.

Something that is going on with challenges indicates we may be missing some needed signaling. Something in the sleep, first_run, new_challenge code is fixing a real problem, but there is probably a better way to go about it.

When removing everything, epic-wallet hangs if listening to epicbox, and a send command is issued. The result is that the generated tx never gets sent to epicbox.

Code submitted here does not have this issue. But I'll be working on finding a more clear and straightforward way to accomplish what this code is doing.