laser x carriage for 20x20 or 20x40 profile

rework on the x carriage of the much4 laser.
See http://www.openbuilds.com/builds/much4-laserv-printed-version.937/
added a holder for a chinese 2.5W laser module.

Also done some rework on the focus adjuster to acommodate this laser module: https://www.thingiverse.com/make:358737

Update 160817: added two holders for guidance line lasers and it just appeared to me they are in line with the laser, making a crosspoint impossible :(
Will remix this evening......
Update: repositioned the l