[FIX] Balance overview: Make currency font clearer

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.
In the native "XRP - Ripple" currency title, the dash was a normal minus
sign. Using an ndash (ASCII 150) looks better.
Why? `em` is scalable, `px` is hardcoded.