Add file copy function on CMenu
copyfile: generate unique default name

file.sch->file_copy1.sch->file_copy2.sch
add warning when copy an opened file
ask user to save changed file when copying
slight change and bug fix

* fix duplicate non-open file will crash application
  reason: finddoc return NULL if file is not open
* Cmenu shows text, change from "copy" to "duplicate"
* make save at right and set it as default
Merge pull request #7 from yodalee/copyfile

Add right-mouse option to copy/duplicate a project file.