Add separator and separator_block_width as universal module options

[cornerman]

It would be great if i3status allowed separator and separator_block_width as universal module options. There already are two such options, namely min_width and align. I think the separator options would be a great addition.

My use case is that I have two volume modules for two different pulse devices and I would like to remove the separator between the two blocks and change the spacing between them.

The separator_block_width property was already discussed as a general directive here, but I think it would be a better fit for a per module option.

[stapelberg]

Sounds reasonable to me. Can you send a pull request?

[cornerman]

Cool, I will work on it!