Round to multiples of shiftwidth
Remove superfluous comment
Adjust backspace, tab, and completion behaviour
Ignore octal numbers when incremting

When using <C-a> on numbers with leading zeros, I don't want these to be
considered octal numbers.
Clear highlighting on common key

I use <C-l> to clear my shell as well.
Remove conflicting mapping

<C-l> is now used to clear the screen. Moreover, I did not use these
bindings lately and only got to note them, when looking at the conflict
wrt. to clearing search highlighting (nohl).
Scroll of to the side as well
Show tabs and trailing spaces
Incorporate options from vim-sensible

These are (as the name suggests) sensible options to use:
https://github.com/tpope/vim-sensible/