show button: send beacon

[Erkan-Yilmaz]

First time users either

• don't know that they need to send the beacon (and other requirements (be in team Gridcoin, ...) to get rewards for their BOINC work) (A) or
• don't like the terminal-way after knowing what to do.

In any case, it would hasten their reward process (considering superblocks are taking long time) when they see a message that shows them what to do (or tells 'em: "click the beacon button")

related:

• startup wizard: configure before launching client

(A) at least the linux users, I remember someone saying in Windows client there may be a hint somewhere

[tomasbrod]

#562

[jamescowens]

This is partially addressed by #1646. When @cyrossignol puts up the wizard, which is coming with the mandatory changes for Fern, this will be closed out.