When curses programs send empty title escape sequences on exit, the
window title would become blank in replace mode instead of reverting to
the initial title. Fix by checking for both NULL and empty string before
falling back to the static title.

Fixes #479

Store and persist window icons in session config files. Icons set via
the command line are now saved during session management and restored
when loading config files.

Also adds error reporting for invalid icon file paths.

Since profiles do not provide a way of setting the window icon, we
re-introduce the --icon option to allow the window instance to report an
icon programmatically.

Fixes https://github.com/mate-desktop/mate-terminal/issues/246

It seems Wayland-based window managers provide additional decorations
that we're not tracking in our "preferred size" computations. This means
every geometry update shrinks the window by a bit.

Factor in the allocated dimensions, not just the preferred ones.

Borrows some ideas from
https://bugzilla.gnome.org/show_bug.cgi?id=769898

I also drop a few unused values leftover from gnome-terminal.

Fixes #350

The `uris_as_paths` member, which is set to `true` when the paste
command has been triggered by the **Paste Filenames** action, was being
checked too late: a file URI was ultimately being entered to the
terminal, as opposed to the expected plain text version.

Test plan:

- Copy a file in Caja, or in any other file explorer that inserts the
  `text/uri-list` and `text/plain` MIME formats into the clipboard.
- Paste the file in a MATE Terminal either via `Ctrl+Shift+V`, or via
  the **Paste** action in the context menu.

Without this change, a file URI is entered. For example:

```
file:///home/jane.doe/my%20pictures/foo%20bar.jpg
```

With this change, a regular filepath [that the filesystem can recognize]
is pasted. For example:

```
/home/jane.doe/my pictures/foo bar.jpg
```

Note that the behavior of the **Paste Filenames** context menu action
remains unchanged (i.e. file URIs are still converted to regular paths
surrounded by single quotes).

Do not show the tab rename dialog when terminal window content is doubleclicked in terminal apps using the mouse

in mailto scheme IDN coding may apply only to domain part
local part if not in ASCII must be unicode

backport of 1c6f8db736efc62d9a9b38bfbc43ec03c8544696
from gnome-terminal

rename some url-related variables
rename TerminalURLFlavour enum to TerminalURLFlavor
backport of 0789b02ee11038743fde08795eb4a1ac0bcc3f47
from gnome-terminal to be a bit close to gnome-terminal source