Add Hidden Group feature

When press "Alt+Tab", the group will not be showed in tabs, if this group
is set to be hidden. This group will be showd only when press the group's
hotkey, and the tabs will show only this group (Use Hide_Other_Group
feature).

Note: Used "EXE" Group for test. Setting file reading logic will be update
in the future.
Make INI setting file name editable

Now we can modify the ini setting file name in "USER EDITABLE SETTINGS"
section in AltTab.ahk file.