Add access to the file and text filters on the meld toolbar

[Angel Ezquerra <angel ezquerra gmail com>]

Hi again,

it would be really nice if meld gave you quick access to your file and
text filters through a dropdown menu (or similar) on the meld toolbar.

Ideally you'd get a text filter dropdown on the file diff views and
the file filter (or both) on the folder diff views. It would be nice
if you could select more than one filter (i.e. if clicking one filter
could check/uncheck the corresponding filter and update the diff
view).

Also, it would be nice if there were a few additional quick settings
buttons on the toolbar itself, such as a show/hide whitespace button
and a wrap/unwrap button. These could perhaps be added to the view
menu as well.

Cheers,

Angel