zsh: Refactor functions

Combine functions{Pre,Post}.zsh into functions.zsh. There is no reason
or sense in splitting the functions like that and differentiating
between functions that should be loaded before and after sourcing the
aliases.

Rename the functions from funcPre, making their aliases superfluous.

.config/zsh/plugins/alias.zsh

@@ -52,10 +52,6 @@ alias feh='feh -.'
 # 'Temporary' shell in alternate mode that does not mess with the scrollback history
 alias tmpshell='tput smcup && zsh && tput rmcup'
 
-## functions
-alias trash=_trash_list_default
-alias nemo=_nemo_wd_default
-
 ## git
 alias gs='git status --short' # overrides ghostscript
 alias gits='gs'