Icons path in new config

[danielwerg]

Currently absolute path has to be used which makes it hard to use with multiple users while using custom icons from home dir.

Suggested solutions:

1. Resolve relative path against ${XDG_CONFIG_HOME}/wleave

2. Expand ~ or/and $HOME (preferred so icons could be shared with other applications and stored in sane dir)

low priority since old css way still works:

#lock { background-image: url("./icons/lock.svg"); }

#14 (comment)