Add Layer count in G-code by default

[reloxx13]

Do not request features for the Prusa3D fork of Slic3r here without confirming it is applicable to the mainline Slic3r, or your issue will be closed. Development builds of Slic3r. Prusa3D Issue Tracker

Is your feature request related to a problem? Please describe.
Missing layer count in octoprint and printer lcd

Describe the solution you'd like
Add ;LAYER:[layer_num] as default in "Before layer change G-code" printer settings
Another solution: add a checkbox for it in the debug output setting. i have gone through all settings and if it was there i would have checked it.

Describe alternatives you've considered

• Add it urself
• Use another slicer

Additional context
Would be more userfriendly if its default, especial for new users.
I just tried out Slic3r and this was the first negative impression - layers are not shown but the print is running now...
Had to google, had to add it, had to make an issue :D

Will also help to debug the g-code.

i see not disadvantages by adding it as default and help new users get a better initial impression of the slicer.

relates
OllisGit/OctoPrint-DisplayLayerProgress#8

Ender 3 Marlin 2.0.x
Slic3r-master.2019.01.15.2253.a4a0d52c.64bit-PR
OctoPrint 1.3.10

[lordofhyphens]

Verbose gcode gives you the layer numbers as well.