This patch adds alternative way of shearing. Currently the user can shear only on x axis. With this patch shearing on y axis is possible too.
To shear on y axis, the user needs to hit alt with shearing. This works in the numeric input mode too.

Current issues to be solved:
If the user uses numeric input and presses alt and lmb simultaneously, it does not confirm. Confirming works only with enter in this case.

Issues to be developed:
Is alt key as an user interface optimal? Should another way be used instead?
Should instructions be printed to header?