Add a preference to hide the $L balance

[Dan-Linden]

Add a preference to hide the $L balance, for the benefit of streamers who don't want to show this info.

Designed solution:
Linden dollar balance will now be obscured by default and appear as "L$ ****"

On mouseover of the "L$" portion of the UI it will show the hover tip "Click to refresh your L$ balance" similar to current behavior.

On mouseover of the "****" portion of the UI it will show a hover tip that displays the actual L$ balance and the text "Click to display or hide your L$ balance"

This can then be a debug setting and not require further UX real estate.

Test Plan

Enable the option and verify it works immediately. Verify it works after relog.
Disable it and verify it works immediately. Verify it works after relog.

[bennettgoble]

Needed: some design/guidance as to where this preference should live. Would a debug setting suffice? Otherwise, where should it go in preferences?

[kylelinden]

Steeltoe and I met and discussed a design solution, it's captured in the main description now.