Line length constraint was added in the constraint tab.
Also was created property grid editing code for all constraints (meaning: line's length, circle's range, rectangle's width and height). Also I've fixed a bug that did not permit to select lines in MetaActions. This bug was because our selection of shapes was done in "face pick" code, and not on any mouse movement.
Based on this work, the single part that is missing are the icons or fixing unexpected bugs that may appear.