Show "Manage Libraries" item in the Tools menu too
Show "Manage Libraries" item in the Tools menu too

This duplicates the entry, so now "Manage Libraries..." is available
in both under the "Tools" menu and inside the "Sketch" -> "Include
Library" menu.

The reasons for this change are:
  - It makes sense for the entry to be there
  - It makes easier for the user to click on the entry

Aditionally, I added a comment about a issue I found with the
newJMenuItemShift function on Xubuntu 17.04 regarding the Ctrl+Shift+K
shortcut.

me-no-dev/Arduino-1,me-no-dev/Arduino-1,me-no-dev/Arduino-1,me-no-dev/Arduino-1,me-no-dev/Arduino-1,me-no-dev/Arduino-1,me-no-dev/Arduino-1,me-no-dev/Arduino-1