[Cashtab] Make sure hide balance toggle also hides XECX balance

Summary:
Currently the "hide balance" switch does not hide the XECX balance bc the colors in the CSS are off.

Patch.

Discovered that the prop is also confusingly named (the implementation is different from the setting) -- so, update that so it all makes sense.

Test Plan:
npm test, see screenshots

Before

After

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D17627