Add the possibility to configure custom separators in the theme file.
These will only be used if the default i3bar separators have been
disabled. Background color will always be taken from the previous
element (to work nicely with my long-term plan, a powerline-like status
line).
Module themes (only!) can now contain state-specific theme information -
for example, the "battery" module has different states for charging and
discharging, and those can have different prefix and postfix
configurations to indicate what is going on.
Individual items in the bar can now be configured with a prefix and a
suffix. It works like this:
* If there is a specific module configuration in the theme
configuration, use that (i.e. { "<modulename>": { "prefix: " a " } })
* Otherwise, if there is a configuration in the "default" section of the
theme, use that
* Otherwise, if the module object itself has a method called like the
required attribute (prefix, suffix), use that
* Otherwise, leave prefix/suffix empty ("")
