Improve "Construct molecule" and "Edit molecule fragment" dialogs

There are several improvements these dialogs require, which could make the clining processing easier:

• Add some shortcuts:
  • "Add" - double click on the row from the "Avaliable fragments" table.
  • "Edit" - double click on the row from the "New molecule contents" table.
  • "Remove" - delete when the element from the "New molecule contents" table is selected.
• In the "Edit molecule fragment" dialog:
  • Replace "Blunt" and "Overhang" radiobuttons with combobox - now this dialog has so many buttons, that it blows the mind of the observer.
  • Disable the overhang, which is'nt active.
• Add new button "Adjust to another overhang" (or some similar name) to the "Construct molecule" dialog. This button should change the selected overhang to make if fit to the other one. This is very required, because sometimes you rather break your brain than pick up the correct overhang.
• Add tooltips everywhere (if needed).