Show line number (v3)

Hi all,

Here's the last branch for the show/hide line feature:
 - set show as default value
 - add cmd/alt/# shortcut
 - somes tabs were hidden into my previous commit so I add a patch to this branch to delete them and at the same time all other tabs from the IDE code.

Since I needed to amend the patch from the v2 branch (https://github.com/supercollider/supercollider/pull/1122), I had to delete it.