Switch to ipython3 / python3

and also fix case when profile dir not detected
and also fix typo in ipython3 get profile inline script
Fix additional typo in inline script
Change default GUI to gtk3

I was not able to find on debian unstable a port of PyGTK to Python3 then switching to gtk3
Preparation to python3 migration: mark bytes strings and use io.open()
Execution of 2to3
Execution of pygi-convert.sh

Meaning converting to gtk3
Update ioscopy.py.in for gtk3 as well
Use (I)Python3 in configure scripts

TODO cosmetic fix: remove Ipython Out[] message from configure output
Fixes to make oscopy start without errors in python3 and gtk3.

Disabled separator in right bar of gtk_figure
Disabled help messages on command line argument
Modified drag and drop to have a Gtk.TargetEntry list on call of drag_source_set
Remove reference to pyplot

According to http://sourceforge.net/mailarchive/message.php?msg_id=31510443 it is recommened to avoid to import pyplot
Fix gettext issue

and remove useless imports (matplotlib, Gtk)
Replace GTK3Agg backend with Cairo backend

and set support_blits to False, and more fixes for Gtk3
Modify default behavior of set_unit

Suppress the case set_unit((_val_, None)) which did set the yunit. Now it is compulsory to explicitly set the two units together.
This avoids a pitfall when yaxis unit is None, meaning a.u.
Fixes around File>>New Math Signal

and also:
 - Display a.u. instead of None in coordinates
 - Trivial GTK3 fix for menu.popup()
Update demo and test scripts

Fix 2to3 issues
Update ounit call to match new behavior (see d06eb18f)
Fix get_iter issue
Fixed File>>Run Netlister and Simulate

However there is still to fix the default selection of base folder.
And update test/update.oscopy to use changecapa and run simulation as per demo/demo.oscopy
Fixes around Windows>>Figure
Update copyright year
Attempt to fix menus - before starting move to GMenu