[FIX] Balance overview: Make currency font clearer

RT-2270 #inreview
In the "XRP - Ripple" text (and in "Bitcoin" too), the lowercase "i"
looked like an uppercase "I", due to bad font rendering with the bold
font. Increase the font size a bit to make the i-dot clear.
[TASK] Balance overview: Use ndash for currency

In the Balance overview, native "XRP - Ripple" currency title, the dash
was a normal minus sign. Using an ndash (ASCII 150) looks better.
[TASK] Balance overview: Use px unit for font size
Merge pull request #1597 from jublonet/feature/2270-balance-lowercase-i

[FIX] Balance overview: Make currency font clearer