[enhancement/ui] Options for bold text, KiB?, and color

[mxvin]

Hi. Firstly Thanks for creating this useful widget :)

I requesting/proposing some visual improvement:

1. Allow text to be bold. QML font.bold
2. Allow to set one color for all text instead of differentiate it based on speed tier (b,k,m,g) -- also, let the speedunit text colored too
3. Text spacing while stacked too close, A quick look maybe it's already reported on another issue ticket
4. For sake of accuracy, I think the correct unit abv for KiloByte for example is KB, not KiB, that means Kibibyte. Your code also referencing kilobyte not kibibyte. Maybe you want to clarify this

Thank you!