i3: Update config

Divide config into different sections and move all relevant lines into
those.
Use the $TERMINAL variable wherever possible.
Cleanup some stuff and add a couple of comments.
Add vim modeline to indicate filetype.
Set the key repeat rate.
Ditch scratchpad-terminal.sh:
    The reason why I created that script was that I liked to have
    different bindings for showing and hiding the terminal. At this
    point it just brings too much overhead in a dirty way for a feature
    I do not really need. mod+space can still be used to toggle focus
    and with mod+comma the window is now shown/hidden from/to
    scratchpad.
Use a terminal flag to set the window name instead of using escape
sequences at the start of a new shell.

.config/zsh/.zshrc

@@ -1,9 +1,6 @@
 ## Author:  druckdev
 ## Created: 2018-11-23
 
-# Set terminals title if this is a scratchpad-terminal
-[[ -z "$SCRATCHPAD_TERMINAL" ]] || printf "\x1b\x5d\x30\x3bscratchpad-terminal\x07"
-
 # Enable Powerlevel10k instant prompt. Should stay close to the top of ~/.config/zsh/.zshrc.
 # Initialization code that may require console input (password prompts, [y/n]
 # confirmations, etc.) must go above this block; everything else may go below.