Switch to tab if file is already open

[murilopolese]

Problem

When opening a file that is already open, you just got back to the editor on the previously active tab.
It should switch to the tab when this happens.

Solution

This following cases are considered:

• Opening a file that is not already open: Open and make it the active tab
• Opening a file that is already open: Make the already open tab active
• Opening many files that are not open: Open and make the first file in the list the active tab
• Opening many files that are already open: Make the first already open tab active
• Open many files that are already open and not: Open files that are not open and make the first the active tab

[ubidefeo]

LGTM