v 3.4.4 Fix issue #17, enhancement issue #10

Z axis slider now moves in 0.1 inches increments when in inches mode.
When begin sending is clicked the program asks if the user wants to set
de current position as zero.
v3.4.4 4-axis, mm/inch fixes, window and widget scaling
Merge branch 'master' of https://github.com/zapmaker/GrblHoming