Dynamic change of settings

[Seeker04]

There are two main (not necessarily orthogonal) concepts:

1. Hot reloading config

For each setting we should investigated two metrics:

• Makes sense to change dynamically? (e.g. startupcmd wouldn't make sense, but border_color or workspaces would)
• Would be hard to implement?

Then based on these, we should decide for which to implement this, if for any at all.

2. Changing settings via menu:list_cmds/0

Another option is to not implement reloading the whole config at all; instead let the user change only some selected settings via the command menu.

[Seeker04]

Related: it might be better to store all settings to globals (or dynamic predicates) with all having predefined defaults. This would make updating them easier and remove the need to always check for existence of optional settings with optcnf_then/2 and optcnf_then_else/3.