More progress bar customization options (0.9.0 - pre1)

[ingdanko]

I love the progress bar changes you made, including the seek option. Here's what is lacking for me in terms of customization.

• Size and color (maybe shape, but not so much) of the seek button.
• • Right now, the seeker is way too big for me. I'm using "small taskbar buttons" which you can find when you right click on the taskbar and go to Taskbar settings.
• • Ability to change the color would be also cool
• The shape of the progress bar. The new update changed the edges to be always round. An option or a roundness slider would be awesome.