Change: rebrand 1.12.0 to 12.0

One question that keeps popping up: "when do we release 2.0?".
NewGRF will force that at least 1.16 will be 2.0, but to not wait
for this, let's drop the "1." and be for ever done with that
conversation.

We are following in the footstep of giants here.

Doc: Removed "FS" from issue number

Because FlySpray is no longer the main bug tracking system.

Doc: Changed several things in known-bugs file

Converted "tabs" to "spaces", changed the order based on the numbering of bugs, made that lines end closer to the 80th character column, changed "Mac OS X" to "macOS", and several other less important changes.

Doc: update known_bugs.txt to include Involuntary cargo exchange with cargodist via neutral station (#6714)

This closes #6114

(svn r21614) -Fix: the spelling of some of the documentation
-Update: some of the documentation