Option to dock sidebar to the right

[brrd]

From #118:

This question is a feature request: the ability to move the sidebar from lift side of application to right. In right-to-left languages such as Arabic and also Persian, it's more comfortable for users to have options in right side.

[thopanX]

This mighg be useful for right-handed people as well. My mouse pointer almost always idles on the right side of the display. Having the panel on the right side might save mouse travel.