Allow indicator offsets to start from bottom and right

[mrnossiom]

Hi,

I like to put the indicator in the lower-left corner of my screen. I do this my hard-coding my current device screen size in my config and then performing offset calculations. This is ok as a solution but doesn't work when you connect external monitors which don't have the same sizes.

I propose to change indicator-{x,y}-position from a uint to a int whose negative values gets interpreted as an offset from the right/bottom.

I don't think this change is breaking.