feat: add seekbar_height and keep_with_cursor options

[Samillion]

Fixes: #623 and #622

Changes:

• Add seekbar_height option. Accepts: small, medium (default), large, or xlarge
• Add keep_with_cursor option back
• Change volume bar tooltip to match volume button

Presets for seekbar_height:

local seekbar_presets = {
    small  = { radius = 1, height = 2 },
    medium = { radius = 2, height = 4 },
    large  = { radius = 3, height = 6 },
    xlarge = { radius = 4, height = 8 }
}

small	medium (Default)
large	xlarge